Most reptile shops will have Beardies, Leos and corns. Why not take your kids and see what excities them. If you want them to be involved in makes sense to involve them from the start.
All the above are good choices for kids to be involved in my opinion.
If your wife is not too keen on the frog idea you might want to check how she is about live crickets in the house chirping away all night and frozen mice in her freezer.