Oh, they know what they're doing. They know exactly what they're doing.
Yesterday, I went to the grocery store with toddler son Charlie. We were parked in front of the store but not going in because there was a crucial at-bat in the Mariner game on the radio. Charlie wanted to go in to the store because why wait. I said to hold on a minute. He thought for a second and launched into a histrionic teary cry, saying he wanted to go in NOW. As it happened, the at-bat ended (Edgar freakin' Martinez striking out) and I went to get Charlie and go in to the store, just like he wanted. When I lifted him out of his car seat, he was clearly thrilled at this event that he thought he caused. He dropped his charade of sorrow, smiled real big, and said "It worked!"
In the future, I expect, he'll remember not to betray the thinness of his little act.