Some apps that I love for kids are from NASA, TED, Library of congress, National archives and the White house.
NASA apps are full of wonderful information in more easy to use bites than their website. I especially like the Earth app with its satalite images of volcanos, sand dunes, glaciers and other large landforms. There is excellent information to go with these images and some time lapse video that shows years of change in a minute or so.
TED is just one of the best ways to find out what new ideas are out there. The fact that none are longer that 20 minutes makes them fit into my schedule. The speakers are excellent the ideas are timely and the stimulation is wonderful.
DocsTeach is a new one that I have only begun to play with. It is from the National Archives and has lessons available in connections with the digital versions of primary source documents. Such a great way to connect students with the real thing!
Another fun one for library and book fans is Storykit. This app lets you create and illustrate your own book. Create the photos and text for a story and then load it for others to read on the website. Easy to use and professional looking product.
There are lots more, but only so many that I can write about here.