My son, also five, had his sports day a couple of weeks ago. He had a lot of fun and seeing his enjoyment made me smile. He didn't really understand why he was doing the various tasks but he had so much fun doing it.
His obsession with space and the universe also makes me smile. He can't get enough of it. I put Brian Cox's Universe on the iPlayer the other week and he sat there for the entire hour engrossed in it. I thought he'd get bored 10 minutes in but he didn't.