This is an old thread but for anyone still interested in this topic, I punched an additional hole in the last pair of grips I got. I was a teenager and I don't think my wrists are excessively small, so it's possible even on the smallest setting they may not be tight enough. Officially you shouldn't punch any extra holes in, but eh. Be careful how you do it.
Edit you can wrap tape around the buckled part or wear another pair of wristbands, etc but I didn't like that. I like them to be able to slide/move a little and just wouldn't like two pairs of wristbands.