I rarely draw children. Part of it's a lack of interest (Sometimes I feel like I need to inform people that ownership of a uterus does not automatically include the 'I love kids' package. Even when I do get this across, some smartass usually says 'Oh, you'll feel differently when you have them.' ... Because having kids when you're pretty sure you don't want them on the assumption that you'll feel differently when the post-partum brain chemicals hit is a wonderful idea.) but part of it is also that kids are hard.
Usually when I begin to draw kids, it goes something like *sketchsketch* hmmm....grrr...too lumpy. *erase**sketchsketch* arrrg! Even worse! *erase* etc. It's essentially the uncanny valley problem. I just think that we are even more discerning though when it comes to children.
And yes, the uncanny valley definably applies to artwork as well as robots. I'm currently kicking around some sort of synthesis involving the theories of Scott McCloud on why we love cartoons so much, the concept of the uncanny valley, and my own experiences, but I'm not really able to talk about it intelligently yet.