Makes you wonder if the kid is even having any fun... Not likely...
Shame, we see it all the time. I think it's the luck of the draw. I've got a first year 8 year old daughter racing, and I was worried about other MX parents ruining this experience for my daughter and I as you described above. We raced in NorthDakota at a race, and the parents couldn't have been better. It was just like you hoped, parents all helping each other shouting encouragement to EVERY rider, not just theirs. Helping kids up, starting bikes for those that couldn't, etc.
Now, a points race in Montana, it was about what you described above, bitching, complaining. My daughter was on an xr50 and this dad next to me gripes that it's not fair that she can shift and likely get the holeshot over the automatic bikes. I looked at him funny and said, look, if she comes out of the first corner anywhere but in dead last, you can have her DQ'd and keep your bowling trophy. We were there to have fun, he was there to win.
The whole weekend was full of stuff like that. The ND crew was all about helping the kids, A rider would tip over and ALL the adults ran over to help out. the MT crew was all about helping yourself, if a rider tiped over, other parents cheered... I don't know how it started, but it's a shame we can't have more races where the kids just go out, ride, and have fun.
I just want to have fun with my kids and offer them opportunities to try different fun things, in this case MX which I enjoy. There are plenty of other places to have fun, people just don't get it. You see some of these young riders, on the edge of control and the parents are still yelling at them to speed it up... sends a chill down my spine to think they don't care about the welfare of their children enough to just step back and watch. You don't have to be Roger DeCoster to see an in-experienced rider on the edge of control.