Arguably Melissa had four and thus they have four, eh?

“Have” is the word you are looking for, “has” isn’t grammatically correct. However, “had” in past tense is also correct, as it refers to the fact that they were born in the past, it does not imply (as you seem to be saying) that the children aren’t alive anymore.

I used to have kids. I still do, but I used to too!

You continue to have kids! :D

sorry I changed to “have”.