There are many free options available in the app store, but this one has been a standby for me because of the "Tap" feature. You should never pay for a metronome!
5 kid-friendly options are listed in the above link
Theory and ear training exercises, glossary, tutorials, and articles (linked). Ideal for adult learners or high school students preparing for music theory exams.
Free PDFs of thousands of classical music scores
If crafting or word searches are your thing, dive in
Try their games "Whack a Note" and "Perfect Pitch!"
Playlists with printable activities
Resources and activities split by age groups: preschool, elementary, middle, and high school
Boston Symphony Orchestra
Students and Educators - high school open rehearsals, competitions, performance opportunities
Children and Families - Interactive and sensory-friendly performances