I'm thinking of taking turns holding my kids under the water to dive for pennies for five seconds.
Are you serious right now? Why would you dunk them to collect change?
I've always done that. They will be all right.
It is wrong to steal change from a wishing fountain. You should find a better activity for them to do.
It's fine, they can survive it and it's my tradition.
While they may be okay, you are making your children believe it is okay to be cheap and steal. You need to allow your children have better things to do than taking coins from a fountain.