I was short on time when I posted earlier, but that Nurture Shock chapter discussed research into why kids lie showed that between 3-4 years is when kids start typically experimenting with lying. I got a real kick out of the research. There's even a conclusion about lying being a more advanced intellectual skill than truthfulness -- it being a developmental milestone, and kids who start lying at two or three do better on academics. I asked my DD8 about lying this morning and she said it's okay to lie sometimes, like to protect a friend's feelings if they ask you a question like about how their outfit looks. Funny how we teach them white lies without even thinking about it. (I did tell her there ways to comment about an outfit without lying.)
That said, at 20 months, I'm pretty sure the others have covered reasons for denying a diaper need -- like they don't want to stop playing, they might not even be aware, or just in denial themselves.
I just had a flashback to the times my kids did things really young and lied, like drawing on the wall or couch, so as not to get in trouble. Then there's lies about who started a fight.
