I like the idea of a lollipop using paint chips but I dk if I'd ever make a card like this though. What an adorable use of a circle punch! Paint chips would be great to punch for these, just pick your favorite colors.
Make the fish out of cardboard or felt, and thread it to the button. For the aquarium, you just need a box. Remove all 8 flaps, then cut windows in the sides and slots for the fish in the top with a box cutter or exacto knife.