Babies have a natural urge to crawl out. My niece made a hole in the playpen to crawl out and her mom threw it away. Before that, her mom thought the sides were high and soft so she couldn't crawl out. When my daughter was 8 or 10 months (can't remember), she crawled out of her cot with the help of the mosquito net hanging above it, when we discovered it she was crying with half of her body out of the cot, her hands clinging to the net and one leg out of the cot. I threw the net away and she could never crawl out of it again.