Yes! Well, my daughter (2 years) is able to pull herself up onto the crib rail so that her torso lies along the rail and one half of her body is outside the crib (one arm and one leg) and the other is inside the crib. Once she figures out how to throw her body weight around a little better, there is no doubt she will be able to climb out - more like fall out - of the crib completely. In our experience, sleep sacks have not hindered our childrens' ability to move, crawl, stand or climb as much as one would think being stuck in a sack would!
T. M.
http://www.theoutlawmom.com