You can take the temperature using the oral, the ear, the anus and the armpit, but the readings do change a little bit in depending on the one used. The difference can be small, however when it comes to a young child even a slightly change in the core temperature could make a difference.
Researches have never found the correlation between the difference in reading and Ear Thermometer Fever Chart will keep you well aware of the differences in temperature. Here it is courtesy of webmd.com
|Axillary/Forehead (°F)||Oral (°F)||Rectal/Ear (°F)|
|Axillary/Forehead (°C)||Oral (°C)||Rectal/Ear (°C)|