Do mermaids give birth to live children or do they lay eggs?

You are talking about a creature ancient mariners did not know what it was so they called it a mermaid.  Lots of sun and no water makes you see funny things.

I believe they saw a walrus for the first time.  That was their mermaid. So the births were live.

They are mammals so give birth in the same way as dolphins 

The question should be is where would those live children or eggs come from since the mermaids don't have any openings that would allow them to come out.

Neither, dummy.  Don't you know nuffin' about mermaids?

Mermaids don't have sex, and they don't lay eggs either.  Mermaid babies are directly delivered, alive and swimming, to their parents homes at night.  They're delivered exclusively by the storkfish.

It's a live birth. At first, it's a fish. But later it grows into a mermaid or merman.

Since they are fictional, they would do whatever the author of the fable decides they would do.

Depends on if they are part maggot or part walrus

mermaids don't exist and you all ready know this

Little known fact: mermaids don't exist.