We used about 8 peeled and sliced apples, 1/2 cup of apple cider, 1/4 cup sugar (or maybe a little more if you don't catch your 2 yo in time), and several good shakes of cinnamon (aim to get it in the pot). I turned the crockpot on low and we left if to cook for about 8 hours. We'd stop to have a sniff every so often and give it a little stir. We let it cool overnight and had it for our afternoon snack. Delicious!
ps...I left a little in the crockpot and left it cooking for several more hours reducing it to apple butter that I will use later this week for our Happy Friday Night Appetizers.