I think "couple" should be fine instead of "married cople". Sounds more natural to me.
Maybe couple is shorter and more handy but I don't believe it is as precise as Polish "małżeństwo”, which is a couple that is married from the legal point of view.
As the English definition of "couple" includes the definition you provided, I'm tempted to agree with awzool on this one.
As far as I know, the word "marriage" is for the state, for the union, but you cannot describe two people and say "They are a marriage".
Even though it refers to two people, the word "małżeństwo" is grammatically singular. Neuter singular, to be precise.
Similarly "rodzeństwo" (siblings) is also singular.
We would rarely say that married couple has a child- always - that 'couple' has a child
Maybe, but nothing about the word 'couple' mentions that they are married, while "małżeństwo" is exactly that - two people that are married.
Yes I understand. But in English, it implies they are in a relationship or married.
I really need to wrap my head around the cases. I would expect "child" to be in a different case since it is a direct object. However, it was nominative. What is a good, clear resource to better understand the cases. I already tried wikipedia.
This is actually in the Accusative case, it just has the same form as the Nominative case - such is the nature of neuter-gendered nouns.
Tamto małżeństwo ma córkę (NOM: córka --> ACC: córkę) -- córka is a feminine noun.
Tamto małżeństwo ma syna (NOM: syn --> ACC: syna) -- syn is a masculine personal noun.
Tamto małżeństwo ma dziecko (NOM: dziecko --> ACC: dziecko) -- dziecko is a neuter noun.
What in the original sentence indicates it I a couple rather than a group of married people?
"małżeństwo" is not some collective noun like let's say "społeczeństwo" (the society) or "młodzież" (the youth, the young people), it refers to one married couple. It can be pluralized, you could say "tamte małżeństwa" (those married couples).