Moglie, this is actually pretty common. There can be different causes, but a common one is all the new stuff they are learning to do. As babies they can stir and go back to sleep. But once they hit the age where they are learning to crawl, stand etc, when they stir they try to practise their new skill and this wakes them up properly. Most of the time it is just a phase and they settle back down. GL, I hope that is true for you.