By age two, you should have a regular routine of brushing the teeth with a small amount of paste, at least once a day, before going to bed. You will need to do most of the brushing, since children have a hard time reaching all the tooth surfaces at this age.
By age three, the teeth should be brushed twice a day, after breakfast and at bedtime. Make sure you use only a small amount of toothpaste, as children this age usually swallow some of it, and you don't want them to get too much fluoride. Somewhere between two and three years of age is when a child should go to the dentist for her first visit.