I think there's two issues here. The first is the kids at the dog park, and I agree that the agency in charge of the park needs to be made aware of the issue.

The other is the mouthing and jumping. Yep, he's a puppy, and that's what they do, but these are behaviors that can be reduced and re-directed through training. My 8-year old lab still mouths other dogs while playing, but dog teeth on human skin is not allowed, and he knows that any play stops the minute that teeth touch skin. We've not had quite as much success with breaking him of jumping up to greet people, but we keep working at it

We were fortunate to find a really good positive reinforcment-style dog trainer at our local humane association, and their rates were super-reasonable.

Good luck!