Gawking and snarling are definitely out. If a spring is in a remote or undeveloped area, it's pretty certain that it's going to be clothing optional. So will glaring at them if you don't approve of skin. If there's any doubt, be courteous and ask. Children and pets are two different things.
Children are entirely welcome in the water.
Common sense would indicate that infants need to have a diaper and plastic pants. Older children should also be observed carefully, as they can become overheated, too. Pets, on the other hand, are a problem. I once found myself sharing a pool with two women and their very large and hairy dog. I had the urge to check myself for fleas.