take it rectal. Just use the tip of the thermometer and no you do it that way until their 6 months and if it's at 100.4 or over its considered a fever. My aunt works at Texas children's and she was telling me that it's the only way to know the right temp. Also make sure if he doeshave a temp that he is uncovered. If he is running it you have take him to the er. Unless he was two months then you could give him Tylenol.