Lily,

 My son (SWCAH) is 2 years old now but he was diagnosed as having low muscle tone as an infant. He didn’t crawl until around 11 months and didn’t walk until around 18 months. He is now running around everywhere but he did have a physical therapist working with him until he was up and running, jumping, climbing, etc. The pediatrician really encouraged early intervention to get him up to speed.