Lost keys

Today I came home from work and did some stuff at home before going to my class. When I was about to walk out the door, I realized that I didn't have my keys. I checked every room I had been in, three times. Could not find them. Finally I gave up, pulled my spare key from my room and went out the garage. I was fifteen minutes late to my class.
Now, it is a rare occasion that I can actually remember the last time I had possession of something, but this was one of those moments. I had left my purse on the stairs, and I almost went outside, but then remembered what I wanted was upstairs, so I tossed my keys back in my purse and went upstairs. This means my keys should have been either in my purse or on the stairs, though they were in neither place. I had the sneaking suspicion that a small person might have helped me lose my keys. So I come home after class and empty out my purse. They are not there. So I turn to the Small Monster and say "Small Monster, do you know where my keys are?" He starts to shake his head no, then breaks into a broad grin and says "They're upstairs in my room." So I ask him to go get them and he comes downstairs with his hands behind his back and says "Pick which hand" I can never decide if I should be mad, or just laugh. Generally I pick laughing.