when he was about the same age...and he'd be giggling the entire time he was running. And we couldn't figure out how to get him to stop. I just always had to keep him in the stroller. This last year, since he's turned 5, he's like a different little boy. I can let him walk to the car from the front door alone (although I'm ready to grab him, if I need to) and he can walk alone in the grocery store, not even holding my hand. Now, if I yell "stop", he will, too, which is a big milestone for him. Of course, I just jinxed us, and now he'll become a runner again!