Anyone who has ever taken care of young children knows how physically exhausting it is.  We also know that the mere presence of kids requires us to move.  When they are infants, we pace the floor at night to soothe fussiness, and walk them in the stroller to help them fall asleep (not a strategy that I promote, but it happens).  We are constantly running after them when they are toddlers to prevent the disasters that can so easily befall them.  Even when kids progress beyond the stage which requires non-stop vigilance and quick reflexes, as my 10 and 5 year-old boys have, there is still a fair amount of physicality required, if you want to keep up with them and share in some of their activities. […]