My 17 Month Old Son And I Were In The

My 17 month old son and I were in the sun most of the day today, he was having fun, drinking water and was fully protected with sun tan lotion. However this evening he had a temp of 102.8, after Tylenol and a bath it went down to 100.5. Could this have been caused by the sun or is it something else? Should I wake him up at night to check his temp?