My son will be four months old this week and has started rolling from his tummy to his back. We are working on transitioning him from the Swaddle Up sleep sack to the one with the zip off arms. He just hit 13 lbs (he was a month early) so we just moved to the bigger sleep sack. Since we started unzipping one arm, he has been kicking his legs so hard during his sleep that he wakes himself up. He will only sleep for 30 minutes to an hour before waking up. Anyone have any helpful tips that might help or helped you with the transition?