Osmo created a great product to combine real life objects and playing on the iPad. Using a small mirror which can be mounted on the iPad front cam the Osmo apps can recognize objects placed in front of the iPad. With the game Tangram you see shapes on the iPad screen which you have to create using real life pieces on the table in front of the iPad.
Check out their website.
Beside Tangram they have a Words app where you can use pictures of letters to form words (learn to read), and a Newton app where you can use all kind of objects to make virtual balls bounce and hit a virtual target on screen.