He learns that he should be shy about it from you guys. Little kids pick up on even subtle reactions. I am sure over the last 18months you guys have mentioned how it smelled bad and he caught on.

I talk in terms of months until they are 2-3 years old. It is just much more representative of where they are developmentally. But I work in pediatrics. For parents it really doesn't matter if you talk in months or years. Although at this age kids clothes are in months so it makes shopping easier if you are already thinking that way.