Budget?Best is probably the FiiO M5 or shanling M0 with a card.$100, Tiny, Use a microsd,support Bluetooth Hi-FIUSB C
There are many cheaper options, if you don't need Bluetooth.
the best would be to get a Fire HD and break the wifi hardware, but not sure how to do it
Parental controls to disable all internet?
easy (for kids/ tech savvy) to override.