Should we begin 'dad' and 'mom' with capital letters?

We only capitalize (begin with capital letters) when we're calling our parents' names for example;

Hi, Mom!
Welcome home, Dad.

BUT,
WE DON'T CAPITALIZE THEM when we say;
- My dad's busy working.
- Is your mom here?
- His mom is pretty.
- Our dad isn't working today.


*more info:
- Religions, nationalities and races of people should always be capitalized.
(Malay, Chinese, Muslims, etc.)
- General subjects at school shouldn't be capitalized.
(mathematics, history, geography, etc.)
BUT we capitalize 'English' in English language.