I'm not going to change seats on a plane to let a mother and her kid sit together.
Why wouldn't you let a mother sit with her child?
I don't know anything about the kid or their background.
The child's background doesn't matter. It is polite to let people sit with their child.
I think kids should learn to sit next to strangers.
I'm not sure the child or their mother would appreciate that. I'd suggest switching seats so the mom can be with her child instead of potentially upsetting the kid.