One thing you may want to be certain to rule out first, before going through changing feed and everything, is going over everything in the kits environment to make sure there isn't something else causing this. I would be looking for possible sources of a toxin, that could be ingested now that they are starting to nibble on solid food. This could be something to do with the nest box, the bedding, the hay, any cleaning agents used, anything that they would have access to now that they are mobile.
If you rule out any environmental toxin, and you're certain about seeing this in other kits, then yes, I would definitely suggest changing the brand/manufacturer of your feed(not just the type), and stop this current feed immediately if at all possible, once you have replacement food. If your rabbits are good hay eaters, it may even be beneficial to pull feed and free feed(unlimited) a good quality grass hay(no mold, no noxious weeds) for a week or two, to help try and stop the build up of vitamin A, then gradually transition them onto the new feed after they've had this short break.
But just know as for any treatment for the kits, there isn't anything you can do besides wait and see if it's something that may correct itself. Though it's my experience that this doesn't usually happen. This is because the toxic vitamin A levels caused genetic problems from conception. The only thing that can be done treatment wise, is for the does and bucks before any future breeding is attempted.
In the case of hypervitaminosis A, the article I posted mentions treating with a vitamin E supplement. This is to help get rid of the build up of vitamin A in the liver, which vitamin E helps assist with. Maybe this could be tried with the kits too, but I don't know as it wasn't tried in the article from what I remember. But if there is very little chance of them surviving, it may be worth at least giving vit. E supplementation a try. Now this is all based on my limited experience through a friend that had the problem, and through research. And it's always my suggestion to consult with a knowledgeable rabbit vet in health matters, and how best to proceed with treatments.
https://rabbit.org/vet-listings/
As for what to do more than just changing feed. If you want you can even take it further, to find other breeders/showers that use the same feed and find out if they're having similar problems. If so, I would contact the manufacturer, though they won't always own up to the problem. I would also contact your state agricultural department. If there is a confirmed problem, the state may decide to do testing on the feed and further investigate the problem like they did with the feed killing rabbits in my state. But you would have to have more people submitting complaints for it to go any further.