I typically wait until I really think they are ready. (Meaning they can tell me they have to go, can pull up and down their pants, and have some desire to use the potty.) I know some have a set age that they work on it, but you'll have to work twice as hard if they aren't ready. So, I choose to wait. My oldest son potty trained right before his third birthday (which is still pretty young for a boy) and my daughter potty trained just before her fourth birthday. Start with daytime, don't worry about the night yet. Skip pull ups, just go straight to underwear. (The pull-ups seem to translate to another diaper in their little minds.) Get to know his routine before you start, it'll be easier on you when you know he always pees about 15 minutes after drinking a sippy cup or always poops after breakfast. You can introduce the potty long before you start actually training him. Let him get comfortable with the concept first. And relax.
at 11:19 AM on Apr. 11, 2011