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I doubt those were roundworms at 5 days old. Likely they were very newly hatched maggots. Do not worm these babies. It takes several days for ingested worms to get to the point where babies would shed them in their droppings.
Instead, change the bedding, give them all probiotics, hang up some fly bags to keep the fly population down (I recommend Fly Relief bags by Farnam - they smell the least bag and, unlike the ones that come with a little dry sachet in the bag, they don't leak).