Thomas Trying to Stand

Thomas has been trying to stand lately. When I'm laying on the bed, he'd put his hands on my body, and lift himself up to a standing position and then he'd let go. He would fall back down and try again. He does this in his crib too, grabbing hold of the crib and letting go. I always yell at him when he does this, because I'm afraid that when he falls, he'll hit his head against the crib poles. I know that he will really get into things when he starts to stand and walk!