I think once a month is fine but they shouldn't really need it if they are indoor bun buns. I could understand if they were running aroung in mud and dirt all day but I assume they don't. You know that the more you wash a dog the dirtier they get. That is a fact. Ask any vet or groomer. The reason is because when you give them a bath it strips their skin of natural oil and if you wash them too often they will make to much oil. THis causes the dirt to stick to their fur making them dirtier. I don't know if it is the same for a rabbit but I think you shouldn't even have to do it once a month.

I wouldn't suggest it more than that though but once a month shouldn't hurt. You shouldn't have to worry about illness if you make sure to wash them when it is warm out, keep them away from drafts while they are wet (and if they aren't wet for that matter), and dry them really well. You can use a hairdryer made especially for small companion animals such as rabbits, dogs and cats. You might be able to get one at Petsmart or something like that. These dryers are not as hot as human dryers which can burn the skin of small animals.

I think you are doing a wonderful job with your bunnies. Keep up the good work! COntinue grroming them every day though.