Pediatric Dehydration Mgmt

We have a pretty nasty gastro going through the schools around here and thus are seeing an uptick in dehydration. This round is mostly vomiting which makes me think it's likely noro. Poor kiddos are vomiting through zofran. Which brings me to my question for the group: When do you use IV fluids and who for? Is it the kiddo who can't keep anything down but looks ok? Do you do it earlier or wait until they're showing more clinical signs (reduced UOP or tears)?

It seems to be a bit preferance and nuance.