Hello everyone. My son has bones (or joint) cracking below his knees w…

Hello everyone. My son has bones (or joint) cracking below his knees when he moves them. It sounds like they're breaking. Someone says it might be due to calcium and that it will pass. The pediatrician didn't say anything, I don't know who to go to, an orthopedist or a surgeon. Do X-rays need to be taken or can I treat it myself?