I can understand it. Too many parents are just plain rude when they bring their kids to various things. They'll bitch about someone bringing their dog and yet their kid is just as much a nuisance or more. Not all parents have this issue, but a little sense would help a lot of them. My biggest pet peeve. Bringing your baby to the movies. Are you kidding me? The kid can't enjoy the movie and all they are going to do is cry at best. Hire a freakin' baby sitter or wait for the movie to come out on DVD.
If you are paying the big bucks for first class, I can see why an airline might try to put a ban like that in place. Not sure if it's right, but I understand it.