Of course PE should be mandatory! Since when are children supposed to sit around quietly and listen attentively for an entire day, day after day, year after year? We are all–children in particular–designed by God to be active, and more than just a 15-minute recess every day. Studies show consistently that physical exercise helps their growing brains. Here is a link to the abstract of a University of Illiois study which used MRIs to link PE to brain development. And here’s a link to a more non-scientist friendly summary of their findings. [I can’t vouch personally for the study, but it is out of a major university, and the abstract is on a government web page, so it’s got to be pretty solid.]
Plus, we need them to develop the habit of exercise for lifetime fitness. How’re they going to do that without being given opportunity to do it?
Besides that, logically, how are our children going to learn to do something other than watch movies and play videos with each other unless they’re given time to do it?