These flash cards address the spatial or positional concepts of front and behind. This concept is much easier to target with actual objects, but flash cards have their place too. I find that this particular concept is NOT well targeted with iPad apps. I've used one where the student drags and drops an item behind or in front of a house, but it's really more just to the left or the right of the house. I do, however, love iPad apps for other spatial concepts like above and below, or left and right.
Try pairing these cards with a fun game like Pop-Up Pirate!