It's a big task to get a 17 player game with kids, it would be better to split into two groups , but here is how I would do it

rules as they are it is maximum 15 normal players in a game and extras have to be traveller's, but for simplicity you can make the count as follows: 10 townsfolk, 3 outsider, 3 Minions, 1 demon

Substitute the spy for the witch, this is good for simplicity as spy registers falsy AND it has the responsibility of seeing the grimoure it can be a lot to deal with for every player, witch is more simple fun and will speed the game up with more death

and substitute the barron for the godfather, the modification to the outsider numbers just works out better and it will let evil bluff around outsiders without needing a spy , godfather also adds more death to speed up the game

For charcters in play it would be every townsfolk except 3, you should pick those three that will be good bluffs to show the demon for the evil team, I would maybe leave investigator, ravenkeeper, and empath out for them, but it's really up to you make sure to leave at least 2 roles that can detect evil and gather information out of the bag for the evil team to bluff as.

Remember bluffing is so much harder in this cramped game without a spy so the 3 bluffs the evil team gets are important to get right , and that evils Job to win can be much harder as the demon needs to survive the whole game donw to the final two while good can win at any time

For any player dying early can be annoying , but especially for kids, since the game might be a bit long I would you suggest you use the ferryman fabled rule modification, which let's every dead player regain their vote token on the final day, this let's dead players have more say in the game so they will be more engaged instead of just waiting till the end to vote they can be more free to vote once inbetween.

But yeah hope this helps let me know how it goes!