The "Mom, I'm bored!" Edition.
My kids don't complain about being bored... much. By the time they finish their chores and schoolwork for the day they are so happy to have some free time that they usually have no problem finding something to do. They've learned that if they tell me they're bored I'll find them something to do that they really don't want to do! But then, my kids are older, and this is something they've grown into. Here's an idea that worked pretty well when they were younger.
Make up a list of all the possible things around your house that kids can do. Include all their games and play-sets, special by-permission-only activities, and even a few random chores that are not on their every day lists. With a little thinking it should be a very long list! Type up your list with a space between each item and then cut up the list so you have each activity listed on a separate slip of paper. Fold the little slips in half and put them in a jar. When the kids get bored they can take a slip of paper. You can either tell them they have to do whatever is on the first slip they draw... or you can let them keep drawing until they find one they like.