Kid going to his first day of school, he looks worried, his dad asks him "What's wrong?"

Nervous, the kid asks, "How long do I have to go to school for?"

"Until you're 18" says the father.

The kid nods, and thinks about this quietly.

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When they get to the front gates of the school, the kid says "Dad, you will remember to come and get me when I'm 18, won't you?"