1) Lie down on bed, on your back.
2) The children will try to crawl onto your tummy, possibly with one trying to make a sandwich of the other one.
3) Grab both children in a hug and commence rolling back and forth on the bed while alternately roaring and giggling.
4) Continue for ten minutes.
They love it, but man! my shoulders and biceps are wondering why the heck I've been hoisting 80 pounds of squirming toddler in such a peculiar way.