How do you easily teach a child to brush his or her teeth?

Parenting isn't easy. Make a game out of it, and tell her that big kids do it every day, include the child when you are brushing your teeth.
Start early. Begin cleaning your children's teeth as soon as they begin to erupt. Make it a game, fun, and remember they don't have the eye-hand coordination to brush/floss for many years, so you will have to supervise, help, and make it an enjoyable daily activity for both parent and child. See a pediatric dental specialist by age 1 for evaluation and guidance.