Hi everyone, my DD is 7 months old, and can only sit unaided for a very short amount of time, and even this is quite hunched over. Bizarrely, the only place she can do this is on a bed. She can't sit at all on any other surface. She is very strong in other ways, and gets around by rolling everywhere. She has strong legs, and when I put her in a sitting position, she refuses to stay in it, and instead pushes up on her legs to do supported standing. She just won't practise sitting at all. She either cries, or wants to do supported standing. Some 5 and 6 month olds at baby groups we go to can easily sit unsupported, while DD just can't. Is this something to worry about?