Build me a city, build me an empire.

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One great way to spur a child's imagination is with building toys. We'd bet that from the beginning of time, kids have found ways to stack things up and knock them down again. Then they move on to building forts, caves, and their own little cities. There really is no end to what they can conjure up. Give them a building set embedded with magnets and you'll be amazed at how many different configurations they can come up with.

We love the Magnetix Jr. Activity System from Mega Bloks, Champlain, N.Y. The Deluxe Set ($29.99) contains a mixture of balls, rods, and various fun shapes, including magnetic parts that can be used as googly eyes, ears, antennae, hats, or a springy tail. In primary colors, the pieces are large, and can be manipulated easily by young hands. The magnets help add stability to the creations and kids can have fun rebuilding their favorites or forming a new structure each time.

The lure of these sets--besides the children's utter fascination with the magnets--is that they are interchangeable and can be used together to create even larger or more intricate designs. The Magnimals kits ($5.99, eight pieces each) add whimsical animals such as a dog, monkey, or dinosaur; Magmobiles ($6.99, 11 pieces), add a car or helicopter.

Preschoolers can enjoy an action-packed thrill ride with the Magtastik Wonder Coaster ($24.99). After the track is assembled (by an adult), youngsters are thrilled as they launch the balls through the tube, watch the cars get lifted by the Ferris Wheel and sent down the roller coaster--only to come...