Things Susan had forgotten about three year olds:

They talk all the time
Sometimes you can trick them into doing what you want
Bedtimes require pre-planning
They have something to say every time you curse
Chicken nuggets
Bubbles get spilled immediately
You push them on the swing till your arms fall off and still have to push them some more
They want to help with everything
They open doors without knocking and peek behind shower curtains
Their conversations can be quite elaborate
They're nice to pick up and carry around