1. Growth and development of 9-month-old babies In the 9 months after birth, babies have completed many growth and development milestones. At this time, the baby\’s height and weight have increased a lot, and his head circumference has also increased. Their motor skills have also improved greatly and they can sit up, crawl and attempt to stand. 2. Dietary needs of 9-month-old babies. At this stage, babies need more solid food to satisfy them.