I had to teach my kid to slide a few weeks ago.
He's in coach pitch, and it just hadn't come up until All-Stars, when suddenly almost any time you didn't slide into second on a force play was an automatic out (the kids at that level finally stood a decent chance of turning a double play).
I showed him a few times on a sloped, grassy hill just to ease him into it, and walked away thinking that I didn't do too bad, and that maybe I could pull it off on dirt if I needed to demonstrate more. The next morning my bottom leg reminded me that I'm old. It not only hurt, my lower thigh looked liked someone had tried to draw blood with a paddle. All thoughts of trying on dirt fled my mind.