There is no reasoning with them until ~3 years old, just diverting their attention.

I think it's important to teach that if someone's sharing something that's theirs, they get to decide how much they share. So I'm usually pretty firm with "this is mine, but I'll let you have some"

It's a two-edged sword though. My 2yo has called me out on the hypocrisy of the "Dad Tax", so I've had to give it up 😭

I tell her I’ll give her a little but I still get most cause I’m bigger and that always works.

On a 4yo that's basically angelic.