Thank you for your query on Healthcare Magic.
Your child seems to have a Viral illness with leg cramps
Some times Myositis
which is a Viral illness presents with high grade fever with leg pains and calf tenderness.
Continue Motrin in prescribed dosage for fever and leg pains.
Rest will give relief from the leg pains.
Give him plenty of oral fluids, Pedialyte
sips to maintain hydration.
Physical examination by the doctor is important and with basic investigations if necessary.
Therefore consult your Pediatrician
for further management.
Hope I have answered your query.