I have not had kids bow hunting yet but have spent many days with them in youth and muzzy seasons. Several recommendations, none of which are mandatory but I have found to help.
1. Something to conceal movement. On the ground - in a blind is best. In a tree - a 2 man ladder stand WITH camo burlap zip tied around the whole shooting rail and stand.
2. Take plenty of snacks and water/pop to break up the boredom.
3. Let them have a phone, book and/or tablet. I struggled with this but man do they stay out a lot longer. They move less too. At 8 years old my son could stay out 3-4 hours as long as his batteries did not die.
4. Warm, warm, warm. Dress them as warm as possible but so they can still move as needed. I actually dress down a little so I can gauge better how the kid may feel because they can't handle near the cold an adult can. Have hot hands, toe warmers and body warmers with you too.
Good luck!!! It is blast to be there when they take one.