My 2yr son got red & white mixed rash on palms, tongue, legs, he has fever too & can't swallow, what could this be?

Hand foot mouth: That would be the most likely diagnosis with the rash on the palms, legs and tongue, combined with a sore throat. Tylenol (acetaminophen) or Ibuprofen will help. It lasts about 14 days. If you want a sure diagnosis, then see the doctor for confirmation.

Allergy to : Some foods may be, the symptoms are associated with allergy, a mild otc antihistamine would help along with a fever reducer if there is any..