My 6month old baby's leg's joint got little cracking sound. it is normal? She seems normal. Is it lack of calcium or any nutrition?

I have read that such cracking sound (similar to the sound of cracking knuckles) is common in children. It could be due to some air that filled up in the joints, and when the joint moves, it would cause the sound. It is not damaging to the child's joints so you need not be too worried.