There's always something to new to learn in chess, I can look at a game from hundreds of years ago or from yesterday and replay the game as if I was there.
There is no mystery to chess, everything is there on the board in front of you, the challenge is to develop the ability to see all the moves, to have the patience to look at all the pieces and their potential and furthermore develop your decision making process. Also resisting the temptation to act on impulsive moves which may, at first glance look good, but then turn out to be detrimental to your game because of something you've missed.
Outside of the game I find that chess players are a sociable bunch, despite the demanding inner processes that the game requires.
I learned the game at 8 years old, I would occasionaly play with friends for fun but did not take the game seriously until shortly before I turned 50, when I joined my local club in Wales in 2012 and won a few games. I asked a regular club member which openings I should play and took it from there.
My passion has grown since then and I've lost many games against stronger and sometimes 'weaker' players, with each loss I try to understand why I lost and do better in the next game.
Kids have a way of stretching my abilities, it's great to give them something I didn't have the opportunity for when I was a kid.
I love teaching chess to my own children and with other people's children I can be well outside my comfort zone as hoards of children make demands from me all at once. Rewards come as I amaze myself and am able to overcome that discomfort and focus on individual needs.
Chess is good for focussing the mind and calming the emotions. I think kids enjoy the game's complexities, the problem solving and mental athletics that the game offers. It's also good for the imagination which has a big part to play in the game.