Now, most of the time we would take the heating pad out of the crib right before we put him in it, but as you can see from the pictures, sometimes we let him sleep right on the heating pad. Let me assure you, the times we did this, we turned off the heating pad before we put him on it. It is safest for there to be nothing in the crib with your child, but if you do allow your child to sleep with a heating pad, please make sure it is turned off first. Use common sense.
Using a heating pad to warm my son's bed worked for me very, very well.