There's an HFMD epidermic right now. HFMD is caused by a virus. The doc can only advise you what to do, there won't be a cure-all med that he can give.
HFMD can happen to anyone at any age, not restricted to the 2-3 yo age group. My adult friend got it when he cared for his son who was down with HFMD too. Just that younger kids tend to be more susceptible to it cos they are not so careful with personal hygiene and go to crowded places like glaygrounds and schools.
Did he have red spots on his bum near the anus?