When I initially purchased this app, I was forced to give a low rating due to a very small but noticeable error (mislabeled planets in the size-sorting activity). After contacting the developer, the issue was fixed. Five stars reflects 1) how glad I am this wasn't $3 wasted on an app we cant use, 2) how glad I am the issues were fixed so quickly, and 3) what a quality (and favorite) resource this has become now that the preschooler can use it!
There are several different activities to choose from. An information activity allows you to scroll through the different planets and listen to a bunch of facts about each one. The size sorting activity allows you to place each planet in order from the sun, like a puzzle, paying attention to the different sizes. It names the planet when you place each in their correct place. This and a video depicting the planets as they orbit the sun, are my sons favorite activities. Then there is the flash card activity. The activity allows the child to match pictures of the planets to one another, then match their corresponding names to each one. This one was a little frustrating in the beginning: the cards need to be placed below the provided examples, then the names of the planets below them. After a little practice, this activity has become very useful - the four year old now recognizes the planet names - outside of the game, even!
Again, great app for fun learning and so glad the developers were easy to contact regarding errors!