I really don't remember when I played Commander Keen last time (eight years ago?), but this genre is really very rare last years. But seems the shareware scene is not dead and LightWeight Ninja should fully satisfy your needs :)  LightWeight Ninja is a fast-paced action adventure game where you take on the role of Ty, the LightWeight Ninja who has been sent on a mysterious mission by his master. Ty is forced to fight a battle of unspeakable odds using all of his elite ninja skills. Although I have no kids yet, I enjoyed this game, it's simple enough, fast , funny and relaxing :) This initial release is a Episode 1 standalone involving 3 chapters. The Chapter 4 and 5 add should be released soon. Download LightWeight Ninja playable LightWeight Ninja Demo (27MB) that  includes level 1,2 and 3 of Chapter 1.