What milestone indicates a child's gross motor skill development at 9 months?

At 9 months of age, one of the key milestones in gross motor skill development is the ability to sit without support. This skill signifies significant strength and balance development as the child can maintain an upright position using their core muscles without the need for external support. Sitting independently allows infants to observe their surroundings more effectively and engage with their environment, which is crucial for their sensory and cognitive development.

While crawling is an important gross motor milestone often observed around this age, some infants may not yet be crawling consistently by 9 months. Similarly, pulling up to stand and walking with assistance are skills that typically emerge a bit later, around 10 to 12 months and 12 months respectively. Therefore, sitting without support is the most significant milestone for gross motor skills expected at the 9-month mark, as it demonstrates a foundational level of physical development that supports later movements like crawling and standing.