This is a really great idea (and honestly, not just helpful for kids but... have you poked your head in some of the beginner's crypto groups lately?), and sounds really fun.
Can I suggest ICX, Icon, for I, or XRB, RaiBlocks, for X? Both are interesting and promising coins.
And if it really needs filling up, I'd also suggest ONION, as it's a great privacy coin
ICX XRB
I'll take all three! Thanks for playing, and helping me fill some of these last slots!