When my daughters were babies we had a shepard mix, had no idea what she was mixed with but she was excellent with the babies. My neighbors were set on having pure bred goldens and they are very aggressive, I know this is unusual for goldens, my point is you just don't know even with a purebred.

Most shelters will allow a trial period also, of course it would need constant supervision.

One good thing about buying from a breeder is a puppy brought up with a toddler may be more tolerant of the sudden movements of a small child.