1. Growth and development of nine-month-old babies Nine-month-old babies can already sit up and even crawl. They begin to become interested in things around them and like to grab and touch things. At this stage, the baby\’s height and weight growth will gradually slow down, but head circumference and brain development will be faster. 2. Nutritional needs of nine-month-old babies. Nine-month-old babies can already eat some soft and waxy solid foods, such as cooked soft and waxy fruits and vegetables.