Cars in bed

I've been upstairs in the study for a little while now, busy putting up a list of books for sale on ebay. I heard a tiny sound on the stairs... what could it be? Hubby is not home, the boys should be in bed. I tucked them both in an hour ago. I went downstairs and almost tripped over Lachie at the bottom of the stairs. It was dark.

"Lachie, what are you doing?" asked me.

"I want to wake up," said he.

"Go back to bed," I said.

"There're too many cars in there. They're racing, vrroommm vrrooommmm"

I went into his bedroom and there on his bed were 26 cars of all shapes and sizes, lined up in a row!

What is your obsession?