Lay your baby on a blanket or wet pad (accidents happen!) and hold his legs in the air, as if you’re changing his diaper. (Of course, the diaper will need to be off at this point.) Clean the thermometer with alcohol or warm soapy water, and prep the tip with a small amount of petroleum jelly to ease passage. Gently insert the thermometer into baby’s rectum no more than an inch. Allow enough time for an accurate reading (follow the recommendations for your particular model), remove the thermometer, and check the results. Trust me, the procedure is much harder on you than it is on baby. He probably won’t be bothered in the least!
Cheat sheet: Spring for a digital thermometer that provides a quick reading—the faster you can get that thing out of there, the better.
Smart advice: If your baby’s temperature reads above 100.4, call your doctor right away.