I've noticed that DS (2.5) likes to lie down fully to play (e.g. with his cars or Brio set). He spends a lot of time fully lying down, often on his side with his arm outstretched and his head resting on the outstretched arm.
So many toddlers / young children do this? (as opposed to just kneeling on the floor to play... though he does do this sometimes too)