I was scrolling through Mamapedia Voices today and came across a posting about sitting http://www.mamapedia.com/article/sitting. The mom was concerned that her child was 6 1/2 months but wasn't sitting yet. I can relate to her concern and wanted to write about milestones and comparing your child with others.
My eldest the first time and never did it again. Seriously. She hated being on her tummy. I was a bit concerned about this but then she started sitting at 5 months and I thought, if she can sit the rolling over thing musn't be too important. And then she sat and sat and sat and did nothing else. She was perfectly content sitting and playing and was not interested in moving. I took her to gymboree classes and tried to get her interested in crawling but she would not go on her tummy. For about 4 months, she did not have any gross motor developments.
Around 10 months she started to "walk" holding our hands and that was it. This was all she wanted to do which killed our backs. She finally walked on her own around 13months and never looked back. The first time she crawled was around 20 months (way behind according to milestones). She is now 2 1/2 and has totally caught up to her peers and I have realised that milestones are a general map for parents but should not be looked at too closely.
My youngest daughter has been rolling non-stop since 4 months and at 7 months just became steady while sitting. She is not interested in sitting. She much prefers rolling around on the floor. I look forward to seeing what route she will take in her development and now know not to worry if she takes the road less travelled :>.