My baby's legs make a clicking sound. What is this?

Q: I keep hearing a strange clicking sound in my 6-week-old baby's legs. What is this?

A: Those sounds are probably caused by sliding tendons, which happen when soft tissue (tendons) interacts with hard tissue (bones). It's very common for a baby or toddler to make clicking and popping noises—similar to the sound of cracking one's knuckles—in the spine and around the shoulders, knees and ankles. These are normal. If your baby makes these sounds in her hips—particularly if they are a clunking, rather than clicking, sound—talk to your pediatrician. You'll want to make sure she doesn't have a congenital hip dislocation, which must be diagnosed and treated as quickly as possible.