J.K.
My son had the side rail until he was about 4 or 4 1/2. We used it for my daughter. She hated the crib and was out of it by 18 months. She has a full size bed. It's only on the boxspring and against the wall in the corner. The opening was enclosed with a king size pillow under the sheets. Despite that she's fallen out of bed a couple times but we had rugs and pillows around the bed too. She reminds me of the whales when they come up and splash down. I've seen her do it. I just recently removed the rail, she's 3 1/2. My husband can't stand the sight of it. She's done okay but I have her sleeping sideways in the bed. I still line the floors with soft cushy things. Seems she's more away if she's near the edge and will right herself. But, she has fallen on the cushy stuff a couple times too. Thank goodness there's cushy stuff. Good luck.