My dd2 is just over 8 months and won't sit up at all, even if I prop her up she screams and flings herself backwards! Should I be worried? Her sister sat unsupported at 6 months and was crawling at this stage, but dd2 won't lie on her front or prop herself up on her hands - she can't roll over either. I am getting worried as she wants to be upright as she is interested in her surroundings and she cries if I lie her down for too long so I end up carrying her ALL the time and its hard with a 2 year old to entertain as well. Is there anyone with experience of this or who has any hints or tips to help her? (She was born on time and is 25th centile in weight). My HV said I should put her on her front more, but she really screams so I feel cruel. Any advice?