Ask HN: Puzzle games for children without fluffy graphics

I'm in search for games my 4 and 7 year old can play that are satisfying, intellectually stimulant and that make them happy. Not the crappy that appears in any search for "games for kids" (I mean stupid games with lots of colors and sound and bouncing pictures of cats). I've had some small success with some 2 or 3 games from https://www.chiark.greenend.org.uk/~sgtatham/puzzles/, plus https://play.google.com/store/apps/details?id=de.stollenmayer.philipp.Pop_1_1_Android, https://play.google.com/store/apps/details?id=com.agc.physicsline, https://play.google.com/store/apps/details?id=com.alexgwyn.slider and http://asherv.com/threes/, but that's all. The experience was not great in any of those games, since they are made for adults, they're somewhat simple to grasp, but then out of nothing they start to add gotchas that I can perceive easily, but not the children (I'm thinking more about the Android games here).