Check for neuromuscular disorders like Spinal Muscular Atrophy (SMA).
Hey friend, not that I have any advices to give but I just want to say we share the same problem, my 15 mo girl is like this too. Is your girl smaller in size than in general? My hubby and I are both like 6 ft asians but my girl's weight and height are on 3 percentile constantly. Sometimes I think it's because of her size that she's unable to stabilize herself during sitting.... So I've just started to give her Vitamin D3 so see if it'll help with her calcium intake that might help her bone or muscle development....
Hi there I just wondering how your little girl is doing I have 14 month old that can sit crawl or walk too we are getting a mri done