Taking a newborn's rectal temperature? Safety first! 1 Use a digital thermometer with a flexible tip. 2 Apply a small amount of petroleum jelly. 3 Gently insert no more than The First Years Multi Use Digital Thermometer Giant Eagle Because It Matters Grocery Store & Pharmacy Hopefully, your baby won't get a fever. But if you suspect your baby is sick, there are a few ways to take a temperature using different types of thermometers. Some are better Badger Baby Oil (4 fl oz)