Walking off of chairs

I had both kids on my own this afternoon. They had their usual wind up time, with BB running back and forth throwing and kicking a ball and LB trying to get in his way. A one year old tackling a five year old makes me tense, but somehow they'll eventually learn each others' limits. LB, in particular, needs to learn some limits. He discovered in the last few days that he can crawl up into an easy chair. This afternoon he started standing up and simply walking off the chair. He is starting to learn to walk down steps instead of turning around and crawling backward. But an easy chair is a little different from a step. So over and over I ran over to "save" him from falling flat on his face. I almost moved the chair downstairs. LB thought the whole exercise was hilarious.  My attempts to look grim and disapproving have so far failed.