The houserabbit society offers a lot of information:http://www.rabbit.org/
You might also want to check in with your vet for info and maybe a little kit with some extra powdered milk etc.
If the litter is really soiled, you should change it, but most of the time mom will eat any babydroppings and keeps the nest clean herself. Then it's best to disturb her as little as possible. If she didn't nest make sure she does take care of the babies and she does lactate enough. Since it's the first nest I take it that both mom and dad are young bunbuns, so she might not be fully adult herself and not know how to take care of them properly. Always pet mom before you handle the babies so your hands smell like her before you touch them. Strange scents and to much distubances around the cage might cause her to neglect or even hurt/bite them. Weighing the babies every day on a letterscale might give you an idea of how well they feed. Mom needs all the food she wants! Keep dad away for a few weeks (also, probably best to take him to the vet for a snip right away, since rabbits do breed like, well, rabbits. Otherwise you'll have a second nest only a few months from now. The babies will be able to procreate also at only a few months of age, so make sure to seperate mom/daughters and sons timely.
Good luck with your babybuns, we might want to see some pics