Ooh, this is an interesting set of comments. I'm currently trying to turn a really old Midimam Keystation 61 into a toy synth for my 3x 10 year old nephews (triplets). I'm using a spare Raspberry pi 4 so it's all gonna be Linux based. But I actually want to make it completely headless because DAWs are too complex and, IMHO, get between the person and the noises they're making. My goal is to hook up a Korg nanoKONTROL2 and use it as the only extra "surface" between the kid and the music. I'm at the very early stages of it right now but I can choose one of 16 midi channels, hit a key and make a noise. I haven't actually done anything with the nano.
I use an RPi4 as the sound generator for the fully weighted 88 key controller my wife plays at home. It runs just one synth - the proprietary physical modelling synth Pianoteq, available for linux, windows, macOS, x86_64 and ARM. It does have a 10" touch screen because the synth has parameters worth controlling (e.g. what piano model). No DAW complexity, but I don't see why you'd ever get a DAW involved with "a toy synth for my 3x 10 year old nephews". It was a little tricky to get the sdcard set up initially, but since I did, it's just power-on-and-play-it.
I think that kids might be interested in more than just a piano, so I wanted to use something like zyn with 16 hand-picked instruments. The nanoKONTROL2 has buttons to play/record/stop, and 8 separate control sections, each with a slider, rotating knob and 3x buttons. I could use them to record into separate tracks and play back solo or together. I just don't know if it's possible to make that usable without a display. That's what I'll be experimenting with. I know that the synth can operate as a VST inside a DAW (eg Ardour) and that many DAWs can run headless (eh hardour) so it may be possible to do this without a mouse, keyboard and screen. The nanoKONTROL2 has LEDs that can be used to indicate status etc.
