There was a large hill behind our place when I was a kid, consequently, we had grass sleds....... two 2"x 1" hardwood runners joined by a narrow foot rest and a wider "plank" seat, if you were lucky you had a piece of carpet tacked on to prevent splinters in your bum
. The bottom of the runners was rounded and shaped......I learnt to use a plane when I was 7 or 8 years old ('57 or '58)......Mum used to save any excess lamb fat so I could rub it into the runners.
I don't know who or when someone "invented" these sleds but there were three parallel tracks running down the hill that were really well worn so the idea had been around for a long time.
It was another time back then, simple fun
.