Crawling is a major developmental milestone for babies that represents both cognitive and physical changes. Not only does crawling allow for the development of baby’s hands and arms, it also helps develop vision skills, spatial awareness, stability, and coordination.

Catherine Workman, MD, clinical assistant professor in the Department of Pediatrics and developmental pediatrician at Hassenfeld Children’s Hospital at NYU Langone, emphasizes to TODAY.com that tummy time is the most important thing parents can do to encourage babies to crawl.

Wondering when you should be concerned about possible developmental delays? By 9 months, your baby should be “sitting or making good progress towards it,” says Dr. Workman. Even if they aren’t yet crawling, babies should be “interacting with their environment, making some efforts to engage with toys around them, and trying to move around and get to things.”

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