The two things robins DO like are fruit and invertebrates, such as worms and insects. If robins happen to overwinter near you, you can offer them frozen or fresh fruit. Favorites are apple slices, raisins, blueberries, strawberries, raspberries, and cherries. Or you can offer them fresh insects. Not to worry.
Mealworms are the best choice, and they're easy to find.
You can buy them at pet stores or through the World Wide Web. Grubco The problem is that it's hard to get robins to notice frozen mealworms. The little wiggling movements they make while they're alive and warm enough are noticeable and enticing to robins. On warmish days, try putting some mealworms out in a deep plastic bowl near a birdbath. Mike Houle of La Crosse, Wisconsin, had robins coming to his yard all winter when it was very cold.