Personally, those rates seem very reasonable and I wouldn't shy from making that more clear.
1) I love that it isn't strictly locked into a subscription model but could be either pay as you go or pay monthly
Paying monthly would remove my stress of his usage and if it was clearly set up as a 'pause any time' subscription model I'd be even more inclined. Ie. He may be REALLY into it for a month or two and then hard pivots to a new thing so being able to pause easily month-to-month while I wait for his attention to cycle back is a great thing.
2) I think you could also explore saying, 'We know AI is moving fast and their models are always evolving, we're committed to offering credits to our amazing community at fair market rates plus a Ball2 platform fee of 10% which helps us improve Ball2 and add more features. And since we're able to pool the buying power of the whole Ball2 community, we hope to keep the cost of creating as low as possible. Currently those rates are...'
I think you're also set up to offer a really incredible maker community as kids share their games and iterate off one another. If you don't have plans for a basic community forum I'd lean in to that. Would be cool to sponsor monthly challenges or organize mini-hackathons where kids spend a weekend collaborating virtually to come up with new more elaborate games or solve design challenges that employ the balls capabilities etc. -- Also helps keep kids engaged and using credits ;) or looking forward to Ball3!
I could also see you offering school stem kit packs or school PE packs etc.
What a really cool space to be playing in.