My little guy is 15 months and he does this... so frustrating. As soon as the nappy is off, he's flipped over onto his tummy and he's sliding of the bed. It then becomes a restling match and he's sooo strong! It takes a lot of strength from me just to get the nappy on decent enough. He's fought free from dh sometimes and the nappy's half slipped sideways when he's toddled off!