"Your answer is considered slang, or too informal or colloquial. Please stick to standard English."
I wish Duolingo wouldn't try to tell me how to speak my own language. Virtually everyone in my area of the country prefers the term "veggies." It's hardly slang at this point any more than "grandma" and "grandpa" are slang.
Wait...did Duolingo not like "veggies" because that's plural? I'd think that "groente" is "veggie." "Groenten" would be "veggies."
Also: If Duolingo doesn't like "veggie(s)" because it's slang, then it also shouldn't like it when we translate "kind" as "kid" (and "kinderen" as "kids"). But it does--so I think Duolingo either needs to loosen up a little with acceptable translations, or it needs to be more consistent.