There is no "best" way to take a 2-year-old's temperature. Each thermometer type has its own pros and cons. Regardless of the type, however, make sure that your thermometer has a digital readout for easy interpretation of the result. It is also a good idea to keep extra batteries on hand.
Temporal thermometers (the ones that scan the forehead and temple) are increasing in popularity due to their ease of use and speed of result. Newer research suggests that temporal thermometers are accurate for children as young as 3 months, so it certainly would be a reliable option for a 2-year-old.
Ear (tympanic) thermometers can be another tool for children over the age of 6 months. This thermometer type is easy to use and can be reliable if it is placed correctly and no ear wax is in the way.
Digital oral thermometers become an option as a child gets older.
Taking a child's temperature can be challenging at any age. The right tools, however, can help make the job easier.
Additional Information from HealthyChildren.org: