Sometimes you have to tell us that something is missing. The ice cream van is not outside the park gates. That's fine. Where it can go wrong is when the writer has an irresistible itch to turn it into a litany. There are no squirming children, no exasperated parents ... Stop! They're not there, remember? What you're doing is an example of unwanted authorial intrusion; you are revealing your prejudices and your specialist knowledge. I don't want to know, not right now. You had me at "the ice cream van is not outside the park gates". Most likely your narrator would not think that way. He or she would notice the absence and possibly think of something much more obscure, which might be related but probably not a social commentary. No?
(I might have exaggerated this one, but sometimes there are egregious examples. Ed)