Simple answer: The beep might not be because they think the cyclist is a child, it's just that the cyclist is illegally running a red light -- something that usually isn't ticketed for cyclists in most areas.

I would definitely honk at another car doing it for sure.

But yes, often times they do treat you like children...sometimes it's good, because they actually will give you adequate passing distance and treat you with some care...other times it's bad when they they try to lecture you about the "laws," even when they are ill-informed (clearly I refer to the "you should be on the sidewalk crap").

I've certainly been hassled by drivers when biking and following the laws...I suppose I do bring it on myself; if I didn't want stuff thrown at me or to be yelled at, I shouldn't be riding a bike (really, my area is pretty bike friendly, but there always are a few jackasses).