Omg I did see the pic on your FB, I didn't realise he did it with his sleeping bag on lol - now thats an art
I was always a nervous wreck when Oliver 1st started climbing, but the more I told him off/deterred him from doing it..the more he wanted to do it
So only thing I could suggest is just to ignore it but observe from a distance
I found that if I allowed him to do it, bearing him mind he was safe and general respect of furniture etc, he soon got bored. It must be so hard though as you have Lewis to think about too.