I agree with Ali, Pornlaw and I think your analogy doesn't really work. There's a big difference between a guy posting family photos and a commercial website posting provocative photos of children.
However, to continue with your question, what if the photos the father posted depicted his children in poses that were obviously provocative in the opinion of the average person. There are other things that going into a decision of what is cp and what isn't. Obviously if my mom were to post a photo of me running around the house naked when I was 3 she wouldn't be guilty of posting cp. At least I hope not or I better tell her to take that photo off of her family photo site.
