This is a little girl who has just learned how to move from lying to sitting independently. There are a couple of ways that kiddos learn to sit up. One is demonstrated here, where the kiddo rolls from their back to their tummy and then moves onto hands and knees and pushes themselves back into sitting. She just recently mastered this skill and is very proud of herself once she is all the way up. The position you see her in at the end is called side-sitting and is a wonderful position for helping kiddos to engage their core muscles while sitting and easily move between sitting and hands and knees, also called quadruped. In addition you may have noticed that she is wearing a helmet to help correct plagiocephaly that resulted from torticollis.