Lingo Legend is the answer to the 'educational game' problem. Most apps are either all education and zero fun, or all game with a thin veneer of learning. This one actually balances the two. It feels like a real indie card-battler, but your 'power level' is directly tied to how well you know your vocabulary.
It isn't a magic bullet that will make a kid fluent overnight—nothing is—but it's a fantastic way to keep them engaged with a language without the nagging. Just be ready for the subscription fee; the free tier is really just a demo.



