Thanks for writing in .
If your son is active and alert , no need to worry. 100 F is only a low grade fever
. Give him plenty of warm fluids to drink( warm water, milk, complan).
Did you mean Meftal-P? You could give Meftal P if the temperature is more than 101.
If this 100 F persists even after 2-3 days, I would advise you to take your son to his paediatrician to rule out other causes of low grade fever with evening rise of temperature.
Hope this helps.
Dr. Divya Kuttikrishnan