I can't decide if my 3.5 yr old understands perfectly but is a stubborn little chap and refuses to play my game, or if he really doesn't understand the concept. I know dd understood it and responded at this age.
Him: I want a snack.
Me: I will get you a snack, but first you have to wash your hands.
Him: NOOOOOOO! I want a snack NOW!!
Me: Yes, you can have one now. You can have it as soon as your hands are clean.
Him: RAHHHHHHH! ARRRGGHHH! What torture you beset me with you tiresome woman. I want it NOWWWWW!
Me: Here is the snack. Here is the warm flannel. Wipe your hands and I will give you the snack.
Him: I DON'T WANT TO WASH MY HANDS I WANT A SNACK!!!!
Repeat for ever and ever about every single issue, large and small, from morning 'til night, and often at various intervals through the night too