How to use old iphone as a music player only without music getting mixed up on multiple devices
I would like to use an old iphone to download music for my 8 year old to listen to. I don't need the phone to be able to do anything else - just want it as a music player. I've taken the old iphone, reset it and deleted all content and settings. Then tried downloading a track to it, but when the track downloads, A. all of my music (which is on my newer iphone) shows up on the old iphone again, and B. my son's music shows up on my iphone. I think it must have to do with apple ID, which I'm using the same one for both phones...? I'm also now worried about my notes and contacts on my phone being deleted or disappearing as I 'signed out' of icloud on the old device to see if that was the problem (I don't need to back up the old phone really, even with the music on it), then pressed 'deleted from phone' for everything. I'm very confused and frustrated, please help!
MacBook Pro (13-inch Mid 2012), OS X El Capitan (10.11.1)