If the fire tablet can install google playstore stuff (as it is customized android after all and you can install google playstore there as well from apk), I will go for the current app thru there (search for io.getcurrent.current on the playstore)
https://play.google.com/store/apps/details?id=io.getcurrent.current
I like it for the kiddos. It has its own custodial little wallet which I load up so they can zap friends, it is a taste of nostr without the global shit well unless the trending posts are penisbutter and so on 🤣 and they can play with the plebai stuff, image generations and so on which can be paid direct from the app's wallet (thinking about it I may go broke on sats with these kids shenanigans meh). If device lost, doesn't matter.