Babies usually sit when they are 6 months old, but the exact timing varies on an individual basis and needs to be determined on a case-by-case basis. Babies have different physical conditions when they are first born, so their development varies. According to normal developmental standards, babies learn to sit, stand and roll over at around 6 months of age, when they will have some behavioral ability, so they will show a willingness to sit on their own. Generally babies basically learn to sit independently at 6-6.5 months, but if a tumble occurs, the baby cannot resume sitting on its own. To get to the point where they can sit on their own without any support, they are usually 8-9 months old. However, if your baby is too far behind, for example, if he or she still cannot sit at 9 months, you should go to the pediatrician for an examination to assess the developmental problems. Parents are advised not to let their babies practice sitting and standing too early, and try to exercise according to the growth process to prevent abnormal bone development. You can add more calcium and protein supplements to your baby and get more sunlight to promote bone development.