Why can't the ducklings go outside? I mean, just short, supervised walks with you might perk them up a bit. Then they can run around, dig, dabble at the grass, find lots of yummy things outside...
As for things ducklings like to do - Swimmies! How old are your ducks? Depending on their age, you could probably adjust a couple of things, but ducks do love to swim. To start, put your ducklings in a shallow container filled with water - a plugged sink, bathtub, or any type of container really. Get them used to the water, and you can put fruit and veggies in the water for them to dabble at - lettuce, grapes (Cut up very small), etc. Make sure it's small enough for the ducklings to eat. Watch the ducklings - don't let them get too cold! They really enjoy swimming.
Umm, here are other things for them:
Unbreakable Mirror - This is fun; it makes it look like there are more duckies!
String - They may chase or bite at a string put above their heads. Don't let them eat the string.
Stuffed animals - Ducklings will cuddle up to a stuffed animal, and may even fall asleep on it! Use with caution, as the ducklings may poop on the fluffy toy.
Treats in water - Ducks and ducklings love to dabble in their water for their favorite treats. You can put almost anything in their water: Lettuce, grapes, cereal,
Toilet Paper Rolls - Ducklings will run and hide in cardboard rolls. Use with caution; if the roll is too small, your duckling could get stuck!
Toss toys - Made from amber prescription bottles with the child proof lids. Drill a couple of holes big enough for snacks or food bits to fall out, and fill with treats!
Feeder Fish - Bought at most local pet stores, these little guys can be dumped into a water-filled container and your ducks will probably love them. Some ducks don’t take to the fish, but most of the little guys go crazy!
Hope this helps! Sorry for the long post lol