If you want something nice and Vibrant, you should take a look at Flame Angels which are a nice red with blue tip tails, or a coral beauty dwarf angle. Mind you, you can only have one or the other, they are both absolutely beautiful fish and will fit in your tank and are reef safe.
A foxface would be okay just mind that there spines are poisonous, you mentioned the tank was inspired by your kids, i know the likely hood of them sticking there hand in the tank is low but for the 1 in a million shot it does happen keep that in mind.
But the harsh reality is on puffer fish is there arent any truly reef safe puffer fish. Mainly because puffer fish eat shrimp and they will absolutely destroy an shrimp you get. And Dogface puffers get pretty big along side being not reef safe.
I haven't found and or read about a butterfly fish that is completely reef safe. But some can be reed safe with caution, with caution meaning they may go after some of your invertebrates, Like a Saddleback or a yellow longnose. They are reef safe with caution. Again, caution usually means theres a good chance they will go after something
A foxface can get real ugly if you like vivid colors. Resting or stressed, they get a very ugly brownish/yellowish color that you will not like. It'll get stressed easily by a yellow tang in its living space with a similar shape and color.
"Life may not be the party we hoped for but while we are here we might as well dance!"