Sorry that you were so upset by this.
I guess I am in two minds. While I agree that the only way to protect your children from being seen by paedophiles on the internet is not to put pics of them on there - but that would close down a lot of mummyblogs.
At the same time, it is a faceless, nameless person who will never ever meet your child.
I worry much more about the possibility of someone in RL endangering my children, and that risk is much higher. Thankfully there are ways of protecting your children (which is something that I keep meaning to blog about, and will try to do so this week).
The fact that someone looked at pics of your boy does not mean that you failed to protect him, just that there are sick individuals out there.
For my blog, while it started as a "mummyblog", it has evolved and I write more about politics and other stuff than I do about my children. I never use photos on my blog that are recognisable and would never use photos of the children unclothed.
Not sure what the photo was, or the search term, but I would say that I do think it unwise to put pics of half-naked children on a blog. I hate that I even think this, because it is horrible to have to hide your children, but there are people who will search for this and that is the only way to avoid them finding them.
I use pseudonyms and only use "son" and "daughter" if I speak of my children. I blogged about it a while ago, might be of interest to you. More on privacy side of things than worry about paedophiles.