I think a kids FIRST disc should be those Gateway Lil/Mini Wizards or other super small diameter super light Gateway Lil disc, you gotta remember, these child hands are small, and a disc feeling good in the hand is one of the main things adults look for when buying our discs.
After they get old enough, I'd get my kids some combo of either Latitude 64 Ruby/Pearl/Diamond in sub 150g weight or that 130 class Innova Wedge that was created for Kids, with any baseline putter and some kind of Leopard or Leopard3 for fairway as light as you can find em