8bitdo has a couple of smaller controllers that are compatible with the Switch that might be worth looking into:
https://www.8bitdo.com/zero2/ — really small, only has a single d-pad but you can assign the d-pad functionality with like a phone app or a PC app to map it to a stick. Might be good for small hands.
https://www.8bitdo.com/lite-se/ — a controller designed for accessibility, the triggers and shoulder buttons have been moved to the front of the controller for easier access and everything is mappable with an app.
I don’t think 8bitdo controllers are compatible with PS4/PS5 but they make for good Switch and PC controllers by my experience.