hot tubs

Here are some things to consider about hot tubs and children:

A hot tub is a body of water in which a child can drown. That has to be first and foremost on your list of concerns. Tubs should be covered when not in use, and provision made to keep small children away from open tubs.
Hot tubs are hot. Small children have much less ability to withstand heat stress than older children, adolescents and adults. Exercise great caution about putting young children - babies and toddlers - in a hot tub. I personally would advise you follow a rule that until kids are out of diapers, they are too small for the hot tub.
Which leads to the discussion of hygeine: diapered children are fundamentally dirty down there no matter how clean you think you keep them. Again, to me this is a good reason to keep little kids out of the tub.
Germs like warm water. Proper chlorination of hot tubs is essential. Hot tub folliculitis is a specific rash caused by infection of the hair follicles of the skin with Pseudomonas, a particularly nasty bacterium. It appears most often in my experience in the areas covered by a tight-fitting bathing suit on a child who sat for a prolonged period in a hot tub.