Quoted from Mottwally:
But, if you're going to have a lot of folks over, and kids will be in the mix. Pull them keys out of the coin door son!!
I learned this lesson the hard way. We had some friends over and their kids wanted to play. I turned on the games and let them play. The adults stayed upstairs while the kids played in the basement. My teenage son was down there so I wasn't worried.
After everyone left I went downstairs to turn the games off and noticed that all of my keys were gone from each game. I freaked out as the keys in the doors were the only keys I had to the games. I asked my son if he knew what happened to the keys and he said "no idea, I was just playing video games".
After looking around the room for a bit I noticed that the keys were in my drink holders on the side of the games. Of course, none of the keys to the games were actually in the corresponding drink holder. I had to find the right key for each game.
Since that time I now have a key locker in a separate room. I know that I could key all of the locks the same but if the original lock and key is with the game, I leave it.
Anyway, nothing wrong with letting people play, including kids. I find that most people are pretty good about taking pointers on how to play, including using one flipper at a time.