You're obviously being biased as a good uncle would be, but no is he very cute. How old is he?
I find that my two brothers (even though one is not particularly child friendly) have some sort of magic touch over my two boys. Whatever they do with them is seen as brilliant even if it's nothing particularly exciting, like you say it seems like an adventure. For some reason if I try the same tactics it never works, but then mum is not seen as being as exciting as uncles

He's 2, 3 early november.
I think the adventure uncle thing comes from not having to really do much of the routine looking after stuff. These last 4 days I've had him I've had to make him some breakfast, lunch and tea, but apart from that it's been freestyle fun time.
It's not a permanent thing, just a childminder illness thing, so it's the extra excitement which helps I think. I'm not exactly a novelty, I see lots of him, but it's still out of his normal routine.
I also don't have to provide him food and stuff, so I've got all day to play lions and football and more lions and robot beepbeeps and drawing and teaching the difference between raw dried pasta and cooked pasta. Spontaneousness.