I've not tried flip booking myself or stop motion animation, but I'm VERY into time-lapse photography using my iPhone. Having recently purchased the 4S, I've been a little bit disappointed in the lack of time-lapse apps that take advantage of the 1080p exporting though. Most of the time I have to make videos in a different aspect ratio and then convert them to 1080p later.
Check out one of my videos using my older iPhone 4 on YouTube. Be sure to watch in 740p resolution. It's not the best video on the planet, but it was a little compilation I put together a while back of some random stuff I shot in early 2011.
For growing babies, I would recommend buying a dedicated tripod for the task, and then setting it up in a specific location in your home where it will not be bothered by other family members, pets, closet monsters, etc. Then place your child (if an infant), or have your child stand in a predetermined location every day, or every few days and take a picture. There are several great time lapse videos of people taking pictures of their children growing up on YouTube, so search around and you might find them.