I would also recommend the preparation H.
Then I would also give this baby (well all of the babies, really) a little plain yogurt. 1 teaspoon per the six babies. They might not like it at first. You can dampen some crumbles with the yogurt and water and let it soak all up to soften the crumbles and feed them this.
Sometimes I've seen babies with pasty vent and partial prolapse because of the reasons Glenda wisely listed. When they have diarrhea, they tend to try to push more out because their intestines feel irritated and they think they have droppings in there when they don't. so they will literally push their vent back out. Sometimes just the right temperatures, a couple of days of preparation H, and probiotics (yogurt) help this.
If it doesn't, then I would still separate the baby to make sure the others don't peck his vent. Give him his yogurt portion. try feeding him a little of the yolk of a boiled egg with that mash - a tiny bit. Then, if you have some, this is the ONE time when you could consider using a tiny bit of neosporin w/pain killer in it. Use that on the vent and push it in. The pain killer will numb his vent and keep him from continuing to push it out. DO NOT let him in with any other chicks that could possibly peck and get any of this on their beaks. Period. He can't reach around to clean himself at this age. Perhaps mix it with the preparation H.
***The 'caine medications are usually very toxic to birds.*** But continued prolapse over more than 2 days in this case can be a very bad situation, so isolating him and using this is one of the very very very rare times I will ever recommend you use it at all. It's worth a shot if the other treatment isn't working and you think it's life-or-death.
Continue his yogurt daily for a week. It won't hurt the others. Then use it for them all weekly (in gradually increasing amounts) during the starter period (1-8 weeks) then occassionally at least during growing (9 weeks to 5 months). Then you can use yogurt weekly when the pullets start to lay.
Yogurt has living bacteria in it (unlike other milk products which are now pasteurized). The lactobacilli in the yogurt colonize the digestive tract. The bird's digestive tract naturally should have bacteria in it to keep diarrhea and digestive illnesses in control as well as helping them to break down food matter into something more absorbable. Babies raised by hens get their living bacteria from her vent and fresh droppings. Brooder raised babies depend instead on us, so I make sure the GOOD bacteria establish themselves by providing some (much more cleanly than a mother hen would) through yogurt.
Doing this and keeping the brooder very clean and dry, and keeping poop out of the feeders and waterers, are also good ways to help keep cocci from causing coccidiosis.
Another hint: raise the feeders up to the level of the chicks' backs when they're 2 weeks old. That makes it less likely that they'll poop in it or walk in it with their little poopy feet.
I hope this helps.
