Cracking sound in hand. Pain at night.

Hi doctor, My son who is 4.5 years old,has this issue,where when we move his hand or leg we hear cracking sound,mostly coming from elbow,wrist,knee and ankle joints. He also complains of pain at knee area(most of time only in one leg),also in leg between knee and feet. Both pain he gets in different legs,like his right gets knee pain then left sometimes has lower area of leg paining. Most of times these pain only come in night,that too after he sleeps as he wakes up and complains of pain. If we run or massage for some time,he gets to sleep but again gets up somedays more than once. Please suggest if I need to worry of something, if so what it could be. I am more concerned about cracking sound in joint than pain at night. Thanks