We had dogs growing up. My siblings and I had tons of opportunities to take care of them and play with them without ever having to go to a dog park (which, actually, didn't really exist, at least not where we lived). It's not as if it's a necessary part of dog ownership. Sure, it's nice, but it's not necessary.
If someone brings a kid to a dog park, and she isn't in a carrier or a stroller (I might even be nervous about those, actually, now that I think about it), the worst that could happen is that a child gets bit and injured, and a dog might have to be put down.
If someone does not bring their kid to the dog park with them, the worst that could happen is that the dog doesn't get to experience a dog park.
I've known lots and lots of dogs who were really good around other dogs and adults, but far less predictable around children. It's pretty common. Sure, there are dogs who hate men or women or blond people, but the owners of those dogs should keep them out of dog parks. We're talking about a really common quirk of many, many dogs, which typical dog park rules allows for. The dog park is their space for them and their owners to not have to worry about that.