We love kids. They taste delicious, but they become bored in a studio very quickly. Also children come with a variety of magical abilities. For example, 8 out of 10 children can locate and push the UPS power kill button in any studio in under 3 minutes from the time they enter. Furthermore, 80% of children are born with 10th degree black-belt ninjutsu skills (they diminish over time, but they'll still defeat you in mortal combat). So, when you try to stop them from running into your sub, they may do a flip and toss you through a wall.
I really don't think any of us mind kids in the studio, but the fact remains a studio is not really a safe place for kids. We have too many cables and items electric that could hurt a little one. And no body wants that.