My son is over 8 months old on 24th he will be 9 months but he still cannot sit himself up I have a chair that he can sit in and doesn't mind it but it seems he can't hold his own weight I've been trying for ages to get him to sit up he can't crawl yet either he was born a month exact early so not sure if this is why ? Anyone have any suggestions on what I can do to help him he's had this chair from 3 months old didn't put him in it until about 4 months i think.