There are some times where I feel I missed out on certain things by marrying my high school sweetheart. But online dating is not one of those things.
I can only imagine your frustration on those sites. In principle I think it would be great, but man I bet there are loons too!
Nothing wrong with a woman that has kids, but it's a LOT of responsibility to take on, especially if you are young.
If you want a MILF maybe just hit up craigslist "casual encounters" section.