Puppy socialization group is meant for puppies under 16 weeks. Dogs are very flexible at this age and it's a key window for socialization. Socializing means teaching dogs to be confident in different environments and to have good social manners with other animals. Letting puppies play with each other is an ideal way of teaching boundaries with other dogs.
This key socialization window also coincides with the age at which puppies are still getting all their vaccines, so a lot of people will try to isolate their dogs until they've finished their primary vaccine series. Veterinarians used to reccomend this, but the American Veterinary Society has officially changed its stance and believes it is more dangerous to under socialize a dog than to expose them to the world before they've finished being immunized.
