No matter what your set designer says - stay away from fake snow/snow machines. It is evil.
I have mounted it twice, both were quite different - the main problem we had the last time was too few fly bars, which lead to using some fancy rope work and stacking back cloths, which was a pain in the rear to fix before every show.
Someone for the kids is a must, as mentioned. As is making sure that there are activities for whilst they are off stage - preferably quiet ones. Depending on your cast, it may be a good opportunity for homework - so you may wish to send a note to parents mentioning that cast members should bring something to occupy their time whilst off stage, and suggest that school homework or a book would be ideal. I also went to the library at the start of the run and borrowed a bunch of books suitable for that age group. If you have the space/facilities, since most kids will be on set at the same time and off set at the same time, maybe you could set up a movie, even if the room is a fair distance from the space - you just need to have one adult with a 2-way radio in the room, and give them a call a few minutes before the entrance.