There is a term used to unexplained pains in young children
"Growing pains is an accepted medical term, though the pains are not due to growing. The typical case of growing pains occurs in a healthy, clinically normal, young child, in the middle of the night, causing intense pain for 10 to 15 minutes in both legs (knees, thighs, calves or shins). Management is simple analgesic measures for the child, and reassurance for the parents that a serious condition is not present."
C&P because I can - it's a term that has been used by my GP and my mum's GP for pains both my sister's had in their legs as kids but for which there was no obvious injuries or treatments available. Pain killers were recommended