There are several Tamagotchi like apps, In Ubuntu Touch(UBPorts) Openstore there's Sakawochi where one can grow fishes[1]. I'm not telling you should get UBPorts for this, but this was one of the Tamgagotchi like apps I tried and maybe an old phone with UBPorts for this app would be appropriate for kids.

[1]https://open-store.io/app/sakawochi.wendigosoft