continue to clean up after the kittens until you start them on solid foods. This is when I let the mom teach them about the litter box. I use a box from a case of soda to train them in as it is easier to climb into. Mom usually does a great job of teaching them. Make sure to keep the kittens until they are 12 weeks so they get all the socialization skills they will need before getting seperated from mom. You will also know they are completly covered by their kitten shots so they won't become ill.
i usually pu the kittens in a play yard. That way mom can get in and out and the kittens are free to roam a little. I use the guinie pig size playyard. I have a samll litter box in there from the start for mom. And she usually teaches them when they are ready.
Good luck with the new kittens. Are you breeding a certain breed? Do you have pictures? keep us posted.
denise