I'm playing other games right now (not WoW), but I don't understand why you had to interject the comment about parent players being a weird combination.
I am a parent and when I did play, I found A LOT of other players who were also parents. The game has been around for so long that a large portion of the population playing it are in their 20s and 30s and that's when people are most likely to have kids.
When they are old enough, they can entertain themselves, and even if they're not, it's not like you're going to be completely wrapped up in taking care of their every need 24/7. Kids sleep. Parents can play after their kids are asleep.
My 9 year old did take some interest, I didn't get her into the game but I let her run around some areas and kill some mobs on my character and it made her happy. So long as she still has a social life outside of the internet when she gets older, gets her homework done and goes to bed on time, I don't see why I wouldn't allow her to play what she wants to.