Peekaboo Barn app (by Night & Day Studios) is my most popular app with my preschoolers. I use this app with a variety of levels - those who are learning cause & effect, sound association, articulation, labeling farm animals, actions open & close door, and greetings hi & bye. When I use an app, it is always tied in to a hands-on activity. In the case of Peekaboo Barn, child may either play with toy animals and/or find pictures of the animal on a velcro board, depending on level of ability. Photos and clip art from Bing Images included.