Why can't they crawl yet?

Here are a few new pics. Don't be fooled by the one I've put up of them holding their own bottles. They will do it for a little while, but not long. I'm trying to teach them to hold their own bottles all the time because it is a pain in the neck to feed them both at once. Limited success so far, but we are making progress.

Meanwhile, Reid finally rolled over from his back to his tummy this week. It was a lot of effort, and he hasn't done it since. I am very anxious for the boys to move on to the next stage. I know that has its own problems, but at least they will be able to entertain themselves and each other a little more.