While in reality, anything soft is nice to sleep in, pajamas are specially made to keep kids safe at night. They do this by being flame-resistant and having a nice snug fit. Not all daytime clothes fit this bill. Often clothing can have buckles, zippers, ties, and other things that wouldn't be very comfortable to roll on top of in the night. Most pajamas also are made to keep from riding up while your child rolls around in their sleep, daytime clothes don't afford that same luxury and may bunch up and be uncomfortable which may wake them up. And let's be honest, we as moms, want our children to stay asleep as long as possible.