Hello, I congratulate everyone on New Year! A question, we're about 8…

Hello, I congratulate everyone on New Year! A question, we're about 8 months old and she can't sit down herself, if you put her down, she sits sometimes falls back, but she doesn't want to sit from lying position, we already passed massage course, crawling also not wants at all, there is no hint of four-legged standing up right away cries as soon as she learns, how did your kids learn to sit by themselves?