From the age of 6 to about 12, my male adult nextdoor neighbour used to lick and suck on my nipples whenever he could. He often used to babysit, but my parents tended to let me go over to his house as well. He was a bit like an uncle.
I didn't really understand it at first, but after the first few times it started to feel quite nice and I kinda looked forward to it. He didn't seem to have any interest in doing anything else with my body, as he never touched my pussy or anything, although on a few occasions (when he must've been especially turned on) he did wank into my mouth afterwards (which I recall not being especially bothered by- it was thrilling to see a grown man's penis and even as a little kid, I didn't actually mind the taste). I think he just really got off on the undeveloped chests of pretty little girls.
He kind of lost interest as my boobs started budding though as I was obviously developing, which was a shame, but there plenty of other boys who liked to play with my boobs after that point, so it was ok. But I do miss those days of being able to help a nice older man with my child's body.