Your child needs to be able to understand that pee and poop goes in the toilet. He or she also needs to be able to interpret the physical sensations that tell them that their bladder and bowels are full.
To potty train, physically, your child will need to be able to hold his or her pee or poop. Your child will also needs to be able to let go of it at will. It is normal for kids to learn to hold their pee and poop before they can figure out how to release it voluntarily.
Finally, in order to be successful using the toilet, a child must be continually aware of the state of their bladder and bowels, no matter what else they are doing. It is quite a challenge for young, busy children to keep two ideas in their heads at one time.
Excerpted from articles by parenting experts Janis Keyser and Laura Davis