At four weeks, the kits should be well on their way to being weaned. Giving them apple as a first fresh food might not have been the best thing, but 2 wedges among so many will probably do no harm. If soft stools or diarrhea should result, give them the LEAVES of raspberry, blackberry, or strawberry or leaves from the lawn weed plantain (Plantago major) or shepherd's purse (Capsella bursa-pastoris)
https://en.wikipedia.org/wiki/Plantago_majorhttps://en.wikipedia.org/wiki/Capsella_bursa-pastoris
If, as I assume, you feed the adults pellets, the kits should have access to them and to fresh water so they become accustomed before mama weans them. Ideally they should have lots of grass-hay as well. Large flake kitchen oatmeal (like Quaker Old Fashioned, though the brand doesn't matter) is also a good food for young kits.
I raised rabbits on a pelletless diet of alfalfa and grass hay, small amounts of whole grain, and as many fresh foods (weeds and safe tree leaves and twigs) as the season allowed. Kits had full access to the adult diet as soon as they could get out of the nest. Doing it that way, I NEVER had any cases of weaning enteritis.
The kits fed this way take a few weeks longer to reach the five pound mark. It's more work than pellets, but a great way to go if you have the time and knowledge. There is a lot of information in the Natural Feeding section, including a list I put together of the plants I used. You pretty much need acreage to make it work.