When kids are learning to sit up one of the ways they do it is to go from their belly into sitting. Just like other new movements, sometimes they need to be shown how to do the movement. Once the kiddo is able to push up on their arms, they can usually begin to learn how to sit up. By giving them a little help to bend at the hips, it shifts their weight backwards. With their weight going backwards they can move their hips over one leg toward the ground. If you help them to move slowly they can use their hands to support their trunk and begin to walk their hands backwards. By doing this and using their trunk muscles to lift up, they move into a sitting position. With your help in the beginning they have increased time to figure out how to motor plan how to use their hands and trunk muscles while moving their hips back and towards the ground. The more they have success with the movement the more they will want to practice moving. Also if they are able to access a toy or something they like once they are sitting its even more motivating to practice the movement.