Final answer:
A child should be able to sit without support by 7 months old, with the normal range being between 5 to 9 months. If they are not sitting by 9 months, referral to a pediatrician may be needed. By 12 months, children often stand with support and may begin walking.
Step-by-step explanation:
A child should be able to sit without support by around 7 months old. On average, babies achieve this developmental milestone between 5 and 9 months. This skill involves coordination and muscle strength. It's normal for young children to reach certain developmental milestones within a range of ages. If a child is not sitting by 9 months, it is recommended to refer to a pediatrician, as they might need early intervention for potential delays.
By 12 months, a child can generally stand with assistance and may start walking. Earlier than that, around 6 months, infants typically can pull themselves into a sitting position. Whenever there is a concern about a child's physical development, especially if they're not meeting multiple milestones, a healthcare professional should be consulted.