My boys (ages 7 and 8) absolutely love the app: Inventioneers on the iPAD. The website says it is for ages 9 and up, but both my boys are doing exceptionally well with the game. They beg to play it. We've started implementing a "read for 30 minutes to earn 30 minutes of Inventioneers policy.
Inventioneers is a fantastic tool for learning about physics and the science behind different features like air, fire, magnetism etc. You have to use provided tools to solve different puzzles. You can also get creative and create your own puzzles.
There is a free version so that you can try this game for yourself. After that, you can make a one-time purchase.) (I am pretty sure it was 99 cents.) There are no other in-app purchases.
If you have a child in grades 1 and up, this is a fantastic way to let them play a game that they don't even know they are learning doing.
Please note that this was NOT a product I was asked to review. I simply LOVE how much my boys LOVE it!