This is a pretty funny shot. You can see the whole picture here.
What I love is it shows how a typical kid runs. Look at the one on the left. His face is all scrunched up and he is trying so hard to win. His body is hunched over at the waist, leaning forward. This is not the way to get fast.
The kid on the right is all loose and smiling. Of course, he’s walking but you can tell he’s having fun. He may lose this race to his older brother, but spiritually, he’s much better off.
A lot of kids think that the way to be fast is like the kid on the left.
It’s not. Even at this young age they can be doing some drills and getting some instruction to work on being faster.
I would have him stand straighter when he runs and to keep his face relaxed. Two simple things that will have a lot of effect when they get a little bit older and start having to run for real.