Let child dictate
often begin to show interest in the bathroom between ages 2 and 3.
Girls often times earlier than boys. When this happens make sure you talk about the bathroom, even bringing them in with you. Buy a small potty if you want and allow them to sit on it (its ok if their clothes are still on) to "practice." don't force it, just go with the flow and make it fun. Reward systems can be good.