From what I've read, children aren't able to control those muscles until they are at least 18 mths old, it is involuntary to them. The American Academy of Pediatrics recommends waiting until your child is 2 years old to introduce potty training. I started potty training my son when he was almost 2. It has been kind of a slow process though because I had a baby during that time, I started watching kids out of my home, and he also had to start wearing glasses and then an eye patch over his stronger eye to strengthen the other eye! All this while potty training. Check out babycenter.com and read all the articles and message boards about potty training. There is a lot of useful information on there including ready signs. (like are they expressing independence, can they pull their pants down on their own, do they have words for potty, do they feel uncomfortable in a dirty diaper and want to be changed, etc) Some children may not even be ready to start trying till they're 3 or later. Slowly introduce it by letting your child help pick out a potty chair, let her sit on it with her clothes on, play pretend with a doll going potty. Get a potty video like Once Upon a Potty (it has a cute catchy song on it). There's no perfect science to it, it should be as natural as possible. Spring/Summer is a good time of the year to start, you can have her run around in just pull ups so it'll be easy to get them off before potty time! Good Luck with everything!