Ask for a rectal temperature in the young child who appears ill. Instruct the parent in how to take a rectal temperature. Ear thermometry is frequently used for measuring body temperature. This technique utilizes an infrared thermometer to take a snapshot of heat emanating from the tympanic membranes. It is fairly reliable if done correctly and with well-maintained equipment. Axillary temperatures are frequently performed on young children as a quick screen. These are unreliable and subject to fluctuation depending on environmental conditions.