I don't know which park you're going to, but perhaps if things don't change after raising this problem of unsupervised children running around the dog park, you might explore other off-leash areas near you.

When we lived in Seattle, we found a book called The Dog Lover's Companion to the Pacific Northwest: The Inside Scoop on Where to Take Your Dog

It has very useful reviews on dog parks in the area, as well as dog-friendly restaurants (usually you will have to sit outside, but sometimes that's better than leaving the puppy at home or in the car!).

Some parks are definitely busier and more popular than others. Might be helpful if you can find a place where Megatron can play without kids invading and being a hazard to themselves and others.