It could just be a way of getting attention, my son does this when he's had enough in that position.
oh yeah! I'd say its normal. Another thing my (weird) babies did was to pull a funny face and shake when they got excited!
My DS used to do it, I think its a normal part of their developement...not really sure what its developing but normal nevertheless haha. We tried to discourage it as we didn't want him to hurt himself
DS does this and he is 16 mths. I read it is for attention so I try to ignore it. He also shakes when he is excited which is really cute
Bookmarks