There's no better judge of a kids' game than a kid. My six-year-old spent a good 30 minutes with Mr. Hat and the Magic Cube. She likes it, so who am I to disagree?
Based on the gameplay, which I tested on Nexus One running Gingerbread, I'd say the game is aimed at ages six and under. Animated sequences begin and run throughout the game. The storyline involves a set of kids who stumble upon a magic cube, and get drawn inside. There they meet Mr. Hat and his crystal wand. Mr. Hat is happy to use his wand to send them home, but just before he does, Dr. Romo flies by in an airship to steal all the jewels from the wand. Your kid's mission is to play the games and solve the puzzles to get the jewels back and go home.
There's a tilt table, which my kid loved, where you guide a colored rolling ball into its matching colored hole. A conveyor belt of letters, where you must touch the missing letter to spell the word that matches a picture. You'll also find a memory game, where you select pairs of identical characters out of a group, and a counting game.
Any complaints? Well, a couple of small ones. There's a second or two of blank screen between the end of an animated sequence and the start of a game section. The game also froze a couple of times when I tried it after my daughter finally handed back my phone. It's worth noting, however, that she never complained about these things. She just laughed when she did well, and groaned when she didn't.