On a related (?) note, I was taken aback by the scene from "Kill Bill 2" ([1]), where Bill makes a sandwich for Bibi and... cuts off the crust. And it was the soft "toast" bread anyway. Doing this was not a thing when I was a kid; actually, eating the crunchy heel of a (Central-European style) loaf was a pleasure.
This is an absurdly common request from small children.
If you don't do it, you may still find them eating around the crusts, for instance if you cut a sandwich in half, or even gnawing through a single point on the sandwich's crust and then leaving behind a crust-rind when they're done.
As a parent, you're then left with no other choice than to eat all of the grilled cheese rinds yourself, so you don't tend to push too hard on the childish habit.
[1] https://www.youtube.com/watch?v=fXXXIokuYGM