> And there's physical limit to how much physical activity one can be doing

Do you hang out with many 5 year olds? They're made of energy.

> I could have him do math but it's a lot more boring

I did Math all the time with my 5 year old and he loved it, but then I also love math, and it's easy to make fun.

Fair points, but understand that this is a multidimensional issue, with each dimension being a continuum.

I know plenty of people using the exact same arguments to argue that kids should not waste time with Lego. There are better physical activities.