Nothing happens. If you adopt, that kid takes over. If you donbt adopt, when you retire you choose a replacement to adopt. I've stopped adopting beforehand because the kid sometimes gets in the way. Plus, if you wait, you get more selection as you can "try again" S many times as you want to get a good replacement.

The cinema is for watching videos to get free coins.

You can't fish but you can catch dragonflies there.

The stamps drop when the customer pays just like the hearts you get sometimes. The stamp page will tell you which levels have which stamps.