I would second the Cessna 152. I trained in one for my IRL PP. I would recommend you grab the free jplogistics 152 mod:
MSFS_C152 Community (V0.9.9!) - Updated: 15/05/2021 - Third Party Addon Discussion / Aircraft - Microsoft Flight Simulator Forums
It really makes the 152 in the sim!
I have been doing some lessons with my grown son, started with the four fundamentals, straight and level, turns, climbs, descents. During these, explained the six pack of instruments and how each is powered and what they indicate.
Good luck, I am sure the kid will love it.