"First came the children, then the adults."
Translation:Først kom barna, deretter de voksne.
"Adults" in Norwegian is an adjectival noun/nominalized adjective, just like "grown-ups" in English. Much like you need to say "the homeless" to clarify the noun status in English, you need the "de" here in Norwegian in front of adjectival nouns like "voksne." It's there to clarify that you're talking about more than one adult.