...when your DD's favorite "reward" for finishing a lesson of homeschooled math is being awarded 20 minutes to "play" more and harder math lessons on KhanAcademy.

...when the preschool child wants to spend all the way home discussion the question, "Why doesn't the car fall off the road into space?" and inserts various mostly-relevant facts about gravity into your explanation, such as that the sun also makes gravity; and you get the impression this isn't a question, it's a pop-quiz.