My four-month old, average-size daughter fell out of my bed because of this sleeper. As other reviews have pointed out, the top of the bed has hard secure sides. But the bottom is contained by nothing more than a light mesh---I think they did it that way so it could fold easily. But because the interior is relatively small, my daughter squirmed (as babies do), and easily slid over that mesh wall. Next thing I knew, she was on the floor. Thank heavens she's OK. You'd be much better off with a sleeper like Rest Assured, which is fully contained by a wall that will keep your baby in (and safe)