When my boy was around 4yo I bought a trail-a-bike for us so he could pedal too.
Now that was a blast! He could pedal and I could coast or if we worked together we could haul ass. He loved saying that "Let's haul ass, Daddy" and then laugh.
But he could coast too. We were out for ride and heading home and I noticed he'd gotten real quiet.
I turned to look and there he is fast asleep and I've just been riding along. Could have lost him on a bump!
Good Times...