This submission is a children’s book about a warring mouse called Fionn. What are the concerns peculiar to children’s books that we need to pay particular attention to?

Title: Fionn
Wordcount: 34,000
Genre: Children’s fantasy
Language:Irish English
Synopsis: A young mouse warrior named Fionn travels to the land of Tara and he and his friends must save it from being conquered by the evil falcon, Lord Malus and his army of rats, weasels, and falcons.
Text: On a small, secluded island on a vast, open ocean, there was a fortified village called Rathrune where a group of mice lived. It had strong-built, wooden houses, a nice view of the sea and the mice who settled there were friendly and courteous.
But along the battlements was a youthful mouse named Fionn. He was moping and sighing to himself while watching his friends playing on the nearby beach and swimming in the water. He envied them. The reason he couldn’t play was that he had warrior exercise to work on with his uncle, Cael who held the position chief of the village. Rathrune may have been his home, but to Fionn, it was a prison.
Fionn heard behind him footsteps approaching. He turned around and saw it was his strict uncle and mentor, Cael. “I’ve been looking everywhere for you.” Cael gave an unimpressed glare at his nephew and student’s manner. Fionn followed Cael as they had plenty of training to do.
They practiced sword-fighting in the back garden of the chief’s cottage. But instead of real swords, the two of them battled with wooden blades.
Fionn tried his best to keep up with Cael while trying to obey his orders he gave out to his pupil. “Have a tight grip on your sword!” Cael yelled. “Look at your opponent, not your sword!” The more commands Cael shouted, the more Fionn struggled with challenging his master.
“Concentrate on your foot paws!” yelled Cael, and he tripped his student and Fionn fell flat on the ground. “I win again,” declared Cael. “But noble try, Fionn.”
Because of another defeat, Fionn punched the earth and threw his wooden sword aside in frustration. He was sick and tired of being pushed around and losing to his uncle.
“Nephew, please just calm down,” said Cael.
“Calm down?!” Fionn exclaimed. “Why am I using up my life when I could be out having fun with my friends?!”
Cael continued to console with Fionn. “That’s where you are wrong, nephew,” replied Cael. “You need to be young to figure out what you’re destined to do. And what is that?”
Fionn had said dozens of times to Cael why he wanted to be a warrior. The reason for his training was to grow into his father. He was a warrior as well and had gone off far abroad to the land of Tara to fight in the war against Lord Malus. But the problem was how can he develop into a hero while being stuck in an old, rotten village in Rathrune? Fionn did nothing since it still frustrated him.
Cael went into the house, leaving Fionn alone. They had done enough practice for today.

Later in the evening, Cael and Fionn’s younger brother, Fergus ate their dinner. Fionn arrived. He thought alone in his room. He came in and sat.
Cael stopped chewing and turned to Fionn. “I want to discuss your training, nephew.”
Fionn looked up at his uncle. “Me too, sir, I’m fit to leave Rathrune and join my father and the other mice.”
Cael shook his head. “No, you’re not ready, nephew. It’s best if you stay here and complete your teaching as a warrior.”
Fionn’s jaw dropped. “What?! That’s unfair, uncle!” Fionn trained for so long and most of his warrior friends shipped away to Tara. Not to mention he hadn’t seen his father since he and Fergus were tiny.
“This is your problem, Fionn,” Cael argued. “You’re impatient.” It wasn’t as though Cael lacked faith in his nephew. Fionn grew into a worthy fighter. He was strong, brave and determined. Cael had taught him everything he knew, and he believed in him. But Fionn needed patience.
Fionn stood up and becoming even more furious. “How can I tolerate when you’re doing nothing except holding me back and never giving me a chance?! What more can I do?!”
He wondered how difficult is his uncle?
“You can listen!” argued Cael. “I’ve raised you, taught you, and taken care of you and your brother ever since your father left on his journey to the land of Tara. I’m the only guardian you have and you shall do as I say.”
Fionn had enough of this quarrel. He rushed out of the room and disappeared from dinner. It was too much for him.

At night when Rathrune slept; alike the chief’s house was silent, Fionn knew this was the right moment to leave this prison he called home which they had trapped him in his whole life. This was no place for a warrior. Fionn packed his belongings, and he changed into a fresh tunic and hoping he wouldn’t wake anyone. He picked up his backpack, and he even sneaked in a few days’ supplies of meals and water. He also put in a knife from the kitchen (which he needed to cut food or as a sword).
As he walked through the hallway, Fionn heard Fergus’s voice. “Who goes there? Show yourself!” Fionn wasn’t sure whether he should speak or keep silent and walk elsewhere. But instead, he whispered. “Don’t worry, Fergus. It’s only me.”
Fergus stopped. “Fionn? What on earth are you…?
Before he finished his sentence, Fionn put his paw on Fergus’s mouth. Fionn brought him into Fergus’s room, for Cael’s bedroom was just at the end of the hall. If it caught them, they’d both be in big trouble. Fionn released Fergus. “What are you doing?” he asked again.
“Keep calm,” shushed Fionn and then he told his brother what he was doing.
“What?” asked Fergus after listening to Fionn’s plan to escape. “You’re going away. Why?”
“Don’t be ridiculous,” answered Fionn.
Fergus knew his older brother was angry at Cael, but he still didn’t realize.
Fionn dropped his supplies. “I need to go,” Fionn said making it sound that this was the last time he’d ever talk to Fergus. “A hero must be free and find his own path. I have a map of Tara.

Editorial comment: This is a pretty good first stab at writing a children’s book. There’s good snappy dialogue pushing the plot along. It sounds as if you’ve started the story at the right moment, when Fionn finally snaps and decides that he’s had enough of his gilded cage of Rathrune and is off to make his fortune.
As an agent I’d be concerned that you haven’t thought too clearly what age your readership is. Talking mice are generally young readers’ fare, but young readers’ books are not 34,000 words long and I’m not entirely sure a mouse in training to be a warrior is going to have a huge amount of appeal to young girls, is it? Perhaps I’m wrong. Reepicheep springs to mind as the most noble of fighting mice in children’s literature that I can think of, but he is an ancillary character. The Narnia series isn’t about him, it’s about the Pevensey children, and beavers and fauns (and lions—sorry Aslan!) are all minor characters.
But let’s assume that you have done your research, you know there is a niche for your subject matter and the story of Fionn the warrior mouse has broad-brush appeal for both boys and girls for children from ages about 8+.
When I look at the detail of the submission, I also have a few suggestions for editing that would make the whole opening quite a bit more streamlined and professional:
The first two paragraphs are pure exposition—scene-setting that I’m not sure we need. I’m not even sure why you start with Cael having to find Fionn to recommence their training. Why not just drop straight into the fight? We can find out later, or during the fight, that it’s only wooden blades they’re fighting with, and that it’s a training session, not a fight to the death.
There’s also a fair amount of “telling” here—elaborately describing feelings and thoughts that can be shown more effectively and immersively by character action. For example: Because of another defeat, Fionn punched the earth and threw his wooden sword aside in frustration. He was sick and tired of being pushed around and losing to his uncle. In the circumstances, it’s quite evident why Fionn would punch the earth and throw his sword around. He has just lost the fight. We don’t need to be told it’s “because of another defeat” or because it’s “in frustration”. To make quadruply sure we’ve got the point, you finish saying again that he is upset because he was tired of … losing to his uncle. At this point you’re beating your reader about the head with a cudgel. “He’s fed up because he’s lost. Do you get it? whack Do you get it? whack Do you understand? whack” Ouch. That repeated battering hurts, and it’s totally unnecessary. Cael trips him. Fionn falls flat. He gets up, throws his sword away in frustration. “Why am I wasting my life sparring with you?”
There are plenty of other small details that are distracting enough, all together, to probably put an agent off. For example Fionn tried his best to keep up with Cael while trying to obey his orders he gave out to his pupil. You need to rethink this sentence. While Fionn is the subject at the start, the pronouns “he” and “his” towards the end belong to Cael, not Fionn. Whose orders?
Cael doesn’t try to console “with” Fionn. “To console” is the verb, it doesn’t take a preposition.
There are tense issues: “But the problem was how can he develop?” should be “how could he develop?” “He wondered how difficult is his uncle” should be “… difficult was his uncle”.
There are some missing words, or poor use of existing words: “How can I tolerate when you’re doing nothing …” How can I tolerate what?
Don’t be disheartened at rejection. You’ve made a great start. I’d do two things before you go any further with this. Make absolutely sure that the story you’re telling is the right length and the right focus for your intended readership. If that means going to the bookshop and hanging out in the children’s section and looking at everything that’s even vaguely similar and working out both what age-group it’s intended for and your best guess as to what wordcount it is (and make a note of who published it, for future reference), then that’s what it takes. You need to be very sure that your book has a market. Then, when you’ve established that it does, start looking at your book as a reader, rather than a writer, and start polishing that prose. Make sure tense is consistent. Make sure all your sentences are perfectly formed. Make sure your verbs are formed correctly, agreeing to their subjects, and that their subjects aren’t ambiguous. If you have any problems with all of this well, there are books, and there are … ahem … editors out there to help.
Thanks for posting!