Thanks! For locking down the iPad – check out Guided Access (Settings > Accessibility). Locks the device to a single app, you need a PIN to exit. Works great with Muky, that's the main setup I recommend.

For speakers, I just got my daughter the Wonderboom 4 – pairs via Bluetooth, sturdy, sounds good. Combined with an old iPad it's a solid setup.

Explicit tag filtering is a good idea. Right now parents manually curate playlists, so you control what goes in. But auto-filtering based on explicit flags could help. Adding it to the list - thanks for the suggestion!