So when my DD1 was about 9mo she had chicken pox,and to itch herself where she could not reach she humped the floor. This was not a problem at the time as I thought once they had cleared up she would stop BUT she didn't! She used to then start grabbing her comfort blanket and doing it. As she got a little older and carried on I tried numerous techniques to try and stop her doing this as I was a little embarrassing especially when people came to the house.I tried distraction and ignoring her,to no avail and now she has no comfort blankets at all. So now she is 3 and still doing this on a daily basis. I have spoken to the health visitor who was very little help and just advised me to try the things I have already done. HELP!!! I also have a DS9 and DD2 of 2years and my DH finds it quite strange. Now I understand that she will be having some sort of sensations down below but this is very embarrassing situation for all involved, especially now my DS is asking why she does it 
any advice will be greatly appreciated.x