"one in four kids": has or have? [duplicate]
Solution 1:
You want to use "has," as the subject is one kid, not four kids. This is the kind of thing where the technically correct version doesn't sound as good to our ears as the alternative, but the logic makes sense if you restructure the sentence: "Did you know that in 4 kids, 1 has an undetected vision problem?"
Solution 2:
Since your sentences refers only to one kid, the verb should be "has."