I am maybe anthropomorphizing them, and I realize they are very simple creatures, but I don't want the chicks to get bored in their brooder. All they had in there was feeder, waterer, one roost, the thermometer we use to monitor the temp, and the sand we're using for bedding. I tried offering them a box of pine shavings to snuggle in, because I thought maybe the sand wasn't cozy enough, but they just cowered in the opposite corner peeping sadly until I took it out. I put a hand-sized rock in there a couple times, thinking they might like to climb it or run around it when they're playing Chase the Lettuce, but apparently an inert rock is too scary, so I took that out, too. But they are slowly getting a little more brave and curious--the last time I tried the rock, they only avoided it, and did not panic like they did the first time.
But I did find one new toy they like: a mirror.
They were cautious at first, but now they love it, and we'll frequently find the three of them all clumped around the mirror and pushing each other out of the way to be closest to it. After a day or two the chicks weren't quite as fascinated with it anymore, but now we just move it to a new location every time we scoop the brooder, and then it is an amazing new experience again. It even seems to calm them down if they can see their reflection in the mirror while we are scooping, like they might be thinking, "Oh, those chicks aren't being eaten alive by the little mesh scooper. We'll be fine, too." I am kind of assuming the real-life chicks think that the mirror chicks are new friends, because 1.) chicks aren't that bright, and 2.) they are very social creatures. I have also heard stories of chicks clustering around stuffed animals or feather dusters.