A friend of mine has a daughter who is too young for a smart phone, but he still wants her to be able to listen to music on the go. I found the following devices using spotify. Have you used any of these or do you have any alternative suggestions?
https://www.tunepat.com/spotify-music-tips/portable-spotify-music-player.html
Edit: found what I was looking for. https://bemighty.com/
Audio nerds have a niche for this, they think (usually incorrectly) that they get better sound quality from dedicated digital media devices than from their phone with a $8 dongle.
But this is good news for you because it means people still make these things! Another commented mentioned Fiio, which is good. You might want to browse around AliExpress, as you will likely find many that are very reasonably priced.