Just in case you needed a reason to NOT post photos of your children online, take a look at this news article from August 2009! A Massachusetts mum finds out someone is using her baby in an adoption scam.
I recommend using a free or premium service like photobucket or flickr to host your photo’s as you can control the privacy settings. However, as much as many people don’t like or trust facebook, they can be used to securely (as secure as anything ever is on the Internet) host your flicks. Just remember that there are 22 privacy settings to date so be mindful to go through all your privacy settings.
If using wordpress or blogger you can also upload your photo’s but post them in a password protected post.
It may not be of great concern if your photo’s aren’t direct head shots of your children… it’s up for you to decide. But please, just be careful and deliberate about all that you do on the Internet.