Here's when and how to care for those little choppers: 1  Even before your baby starts teething, run a clean, damp washcloth over the gums to clear away harmful bacteria. 2  Once your baby gets teeth, brush them with an infant toothbrush. 3  Once your baby's teeth touch, you can begin flossing in between them. Around age 2, your child should learn to spit while brushing. Avoid giving your child water to swish and spit because this might make swallowing toothpaste more likely. Kids ages 3 and up should use only a pea-sized amount of fluoride toothpaste.