Khan Academy Kids is completely free - no ads, no subscriptions, no premium tier. Ages 2-8. Covers reading, writing, language, math, and social-emotional learning through interactive games, books, songs, and activities. From the nonprofit behind Khan Academy. If you're looking for one educational app to install and forget about paying for, this is it.

Free. Actually free. No ads, no "unlock premium," no "subscribe for more levels." Khan Academy is a nonprofit. They don't need to monetize your kid.
Ages 2-8. The curriculum covers early literacy (letters, phonics, reading), writing, language development, math (counting, addition, shapes, patterns), and social-emotional learning (feelings, relationships, self-regulation). Thousands of interactive activities, animated books, songs, and games.
The adaptive learning engine adjusts difficulty based on your child's performance. If they're breezing through letter recognition, it moves them to phonics. If they're struggling with counting past 10, it gives more practice. No parent configuration needed.
Compared to Duolingo ABC (also free, ages 3-6, reading only), Khan Academy Kids is broader. Duolingo ABC goes deeper on phonics and reading. Khan Academy covers reading AND math AND social-emotional learning. For a single educational app, Khan Academy Kids covers more ground. For focused reading instruction, Duolingo ABC is better.
Compared to paid apps like ABCmouse ($13/mo) or Homer ($10/mo), Khan Academy Kids offers comparable or better content for free. The production quality is high - animated characters, professional voice acting, polished games. It doesn't feel like a free app.
Available on iOS, Android, and Amazon Appstore. Works offline for downloaded content.
The only thing it doesn't do: progress reports for parents are basic. No detailed analytics on what your child has mastered. You kind of just trust the adaptive engine. For ages 2-8, that's usually fine.