Well, you could just get an Apple. New plus boards are being made, the cards you need are available.
Mine is equipped with:
80 Col / mem expansion to 128K
Fast Chip for some speed, up to 16Mhz (which is crazy fast on most software designed for 1Mhz)
HDMI output device, VidHD card. This thing is GREAT.
CFFA / USB Flash disk solution for loading programs, disk images, etc...
My younger granddaughter enjoys the machine. I've got a joystick on it, and am seeking a mouse card. Those are a PITA right now, and I may just build one.
I need a printing solution and that's true for my home overall right now. Gotta break down and get a good printer. I just hate doing that. Need to talk to some people and get one I won't get pissed off at.
Right now, we play games, education and action, create with the various programs, painting, etc... She enjoys time on the machine and soon will write some little programs.
LOGO is just too much fun for little kids. I can't wait to see her try it. And with a little speed boost, the machine should really perform!
That all said, my mind goes right to the Raspi 400. It's a pretty cool little computer, built into a keyboard, has the right ports, etc...
If you do some setup on that thing, a younger person could have a good time, and could by the way run an emulated Apple and have a good experience.
I see billziss talking about building the Ben Eater 6502. This is something I would enjoy with them. And if successful, that is a powerful experience on par with anything we had back then.