Is chlorine harmful and is it serious if, for example, he gets a little water in his mouth when he puts his hands in?

Hello and thank you for your question,

In fact, the spa is not suitable for a child (let alone a baby), because it is much too hot and as they have a small body surface to evacuate the heat it could be very dangerous.

For a pool, it's okay, and just with her hands going into her mouth, I don't see a problem here. I would limit it to a few minutes though, so no prolonged swimming.

To cool baby down, the best way is with a warm bath.

Have a nice day!

Emmanuelle