What Causes Pain In A 2 Year Old's Leg?

Hi Doctor my daughter who is 24months old,often wake up at night and says tht she has pain in her leg,its a kind of leg cramping,is she suffering from any disease,she is a very healthy child,never had any fever,diarrhea or cold,her immunity power is very strong,because I pay very special care for her food and everything.kindly help me