Kinship names are the words we use to indicate family members, like mum, mom, dad, aunt etc. Incorrect capitalisation of these names is a huge bugbear of mine. I see it done incorrectly in so many self-published books, and more and more in traditionally published books too.
It seems to cause a lot of confusion, when it’s really actually very simple:
Capitalise when the name immediately precedes a personal name, or when the name is used alone in place of an actual name.
So:
Did you remember to get Mum a birthday card?
We went to see Dad when he was in hospital.
Lily and Joe loved visiting Aunt Susie’s house.
I was seven when I last saw Grandma.
Don’t capitalise when these words follow the personal name, when they don’t refer to a specific person or when they are used with possessive nouns or pronouns.
So:
The Sinfield sisters always stuck together.
There aren’t many dads who would do that.
My aunt wasn’t feeling well.
I bought a card for my mum.
Sally’s grandma lived next door.
Many children’s books portray families and use these terms and I shudder each time I see it done incorrectly. Children learn from the books they read. It’s up to writers and editors to make sure we get it right.