Spincasting would probably be the easiest. Push the button….turn the crank.
My kids use spinning reels though. We use Abu Garcia Cardinal SX 5’s & 10’s, Shimano Sienna 500’s and a Sedona 1000. I also just got an Okuma Avenger ABF 30b (with baitfeeder switch) for pike. I don’t see my kids having any troubles learning that. Kids are smarter than most adults lol.
Spinning reels are easier for kids to learn in the winter because they aren’t casting. Flip the bail….close the bail….turn the crank. Not far off from push the button….turn the crank. Having them manually close the bail each time will also teach them proper practice for when they do start casting with spinning reels.
Pretty much any decent size 500-1000 reel should work well. Might have to consider replacing the gear grease with some quality reel oil if you plan on fishing outside a shack to reduce stiffness.