Mobile VS immobile

This is 1 of the typical days. Kody(mobile) would crawl to side of Karissa(immobile), then take away a toy that Karissa is playing. Karissa has no way to grab it back. Cuz she would just sit still. No matter how hard she rocks her bottom back & forth. She would still sit at the same place. Take a closer look of where Karissa sits in photos, and you know it's true that she stays in 1 place.