The recommendation of the American Academy of Pediatric Dentists is to start using a fluoride toothpaste as soon as your child gets his first tooth.  However, it is very important to use a small amount – a smear about ½ the size of a grain of rice.  Young children aren’t good at spitting out toothpaste and will likely swallow the toothpaste as you are brushing them; but if you use the very small amount recommended then it’s ok of they don’t spit.