LEGO Series, or LEGO Creator Island
If you have young kids or children that always want to play or download a new game, give them some LEGO games. There's a big collection of LEGO titles on the Google Play Store that are completely free. Yes, they do have a few paid games, but most of them aren't.
Our first choice is LEGO Creator Island, which is somewhat similar to Minecraft for kids, and it's free. That's just one of many though, so we recommend heading to the app store and looking through everything they have to offer.