Agreed with pus and Saint. With a parent who is an established player and known by the community, there shouldn't be any issue. I'm sure that most game hosts would be more than happy to allow that, with the caveat being that the kid is under the adult's supervision at all times.
While my son is too young to play, he's attended a couple of games with me at the Mill and locally here in Kingston. He didn't want to play, but he did love being there around all the guys with their gear and guns. Turns out for a 10 year old, he got a hell of a lot of attention at the Mill when he pulled out his TM M4 Boys to show off, all while handling it safely, finger off the trigger, etc... It was a lot of fun for everyone. And I seriously look forward to the day I can play an actual game with him.
However, before you kiddies decided to drag mom or dad off to the airsoft field with you in hopes to play, remember they have to be actually playing with you as well. Dropping you off doesn't count! And a parent unknown to the player community is not likely to make any difference to a host.