I've noticed that 'y' is almost exclusively used, but in some cases 'e' should be used instead. I'm basing this on Duolingo so I'm not sure if it's correct, but here are some examples where it requires 'e':
- Padre e hijo.
- Quiero hijos e hijas.
What is the rule for determining when to use 'e' as opposed to 'y'? Is it specifically when talking about family, or is it something else entirely?