Big to nuff?

Everyday I drive the middle school kids to school. Jacob rides with me. He is always so excited when we pick up our carpool. He makes them laugh on most days. It is a delightful drive... Until we drop them off. He asks me, "Am I big to nuff?" and when I have to tell him he is not yet big enough to go to school he feels sad. But he seems to get over it pretty quickly.
Then I get home and help the elementary kids get ready. They like to walk to school so Jacob doesn't seem to make a big deal about them leaving.
When we take Joshua to school Jacob grabs his back pack and declares "I'm big to nuff now." I don't say anything because I need him to get into the car in a cooperative mood. We pick up the neighbor kid and off to school. The boys jump out and realization hits that another day has come and he does not get to go to school. Melt down. Serious screaming and crying. I feel bad for the kid. He doesn't realize that he still has 3 more years before he gets to go to school.
And then I think it might be me the one who cries when they are all in school.