Before your baby's teeth come in, use a wet cloth to gently wipe off the gums. Once the teeth emerge, use a soft children's toothbrush with water or non-fluoride toothpaste. When your child turns 2, you can switch to fluoride toothpaste.
Brush your child's teeth at least twice a day. You'll have to do the brushing, or at least assist with the brushing, until your child is about 5 years old.