Capitalization

[Stephen]

When I was born, Mom was forty and Dad forty-six...
"Hey, mom," said Billy, "what's that around your neck?"
Hey, Dad, what's for dinner?
My dad doesn't like going there.
Source: COLLINS COBUILD ENGLISH LANGUAGE DICTIONARY, First published 1987, Reprinted 1988 (twice), 1989

She lives with her Mom and Dad.
My mom got this for me. Source: Longman Dictionary of Contemporary English, Third edition with New Words supplement 2001

When should we capitalize mom and dad?
Thank you very much for your reply.

[Alan]

Normally only when used as proper nouns (i.e. without a preceding determiner such as 'my'). Usage is, however, not absolutely fixed on this point, as you can see.