They should sit by 6 months, but my daughter didn't and the health visitor was bugging me that I should teach her. she started sitting after 2 or 3 weeks of me trying to encourage it, but only properly sat up from.lying on her back about a week ago, until now she rolled onto her tummy and sat up form standing on hands and knees each time!

My daughter is 8 months and only started doing it not long ago, no sign of crawling yet either x @rachmyers95

It really varies. Average age I'd say around 6months but I've had plenty between 7-9months at nursery who couldn't sit up. Max could around 6months but he would often still fall back.