When a ‘baby' rabbit is found, often it's exactly where it's supposed to be. A mother rabbit only returns to her young once a day - and that's typically at midnight to 2 a.m., to feed them. Yes, they are fed just once a day (night).
If the bunny was in a secluded area or burrow (under or in a log/tree, brush or bushes, etc), especially with other babies, chances are the mom will be back. If you can keep your dog from going to this area over the next couple of weeks, it would be best to just put the bunnies back.
One of the most common mistakes a well meaning human makes is to feed the baby too often and the wrong thing. Since this is a wild animal, they will often seem ‘fine' right up until they pass away. It's a survival instinct in the youngest of them, to hide symptoms of disease and illness. Perhaps one out of ten baby rabbits attempted to be raised by someone untrained, will make it.
Obviously you know that keeping a wild rabbit is illegal in many states. If a rabbit is a true orphan or rescue, it's necessary to call a wildlife rehabilitator. In some instances, in some states, if you have a background caring for small animals/rabbits and this can be referenced through your veterinarian, you may be given instructions, provisions and allowed to care for the rabbit with regular visits by someone in rescue and rehab.
More details about baby bunnies in the wild are here
To find your local wildlife care center or preserve, call your humane society for information; calling most vets in the area should also be able to render information and phone numbers to call, as well as calling local animal control offices.
So, the best thing to feed them is nothing. If they've been more than 24 hours without their mom, you might offer a few drops of plain water via eyedropper, but a professional rehabber is absolutely necessary for anything more than this.
Good luck with them, no matter what choices you make - you've got a big heart and wonderful intentions. Thank you,