When deciding on the best thermometer for your child, it is vital to consider the following three age groupings. Zero to 3 months. If your child is within this age bracket, use a digital rectal thermometer to take temperature readings. Besides, some research findings indicate an artery thermometer might be useful in giving accurate temperate readings for children within this age. Three months to 4 years of age. If your child is within this age group, a digital thermometer can be used on the armpit. Besides, you can use an artery thermometer to take the temp readings. However, you will have to wait for your toddler to get to 6 months before you use an ear thermometer to take the readings. When you are in doubt of any temperature, reading always takes rectal temperature measurements. Four years and above. When kids are four years of age and above, you can train them to place the thermometer below the tongue or the armpit. Besides, you can use a digital ear thermometer to take an accurate reading.