Is this said to indicate the child is the youngest (most recent), to indicate that they intend to have no more children beyond this one, or both (and dependant on context)?
It can mean both, although without context I would argue that it would be understood as the latter translation, and for the former one would rather say to nasze najmłodsze dziecko (‘it is our youngest child’).
But I agree that in general it can mean both.
That's valid interpretation, but one of few. Or maybe „the pair” decided not to have any children more. The least probable is that the child is „most recent” one, but usually one would say 'the youngest”.
"This is...", not "It is...", unless the child is dead. Translators confuse it/this all the time, it is one of my top ten most common edits.
I thought ostatnie dziecka would be more correct because someone in the discussion said all words denoting an amount of something need genitive. ???