Physical development includes children's gross (large muscle) and fine (small muscle) motor skills. Physical development can be taken for granted because it is often assumed it happens automatically. After all, our kids just keep growing. However, as adults we can do a lot to help motor skills along.
Getting them outside, both at school and home, is important for arm and leg development. Practice running, jumping, hopping, galloping and skipping with them. Get a light ball and practice throwing, kicking, and catching. Get them a tricycle for peddling practice. Just a little bit regularly really helps them along (I'm not thinking boot camp).