Another poster suggested you feed your Mother rabbit 'Oats'. Do NOT do that. Rabbits and oats don't mix. They can harm your rabbits kidneys. Feed rabbits Timothy hay, Timothy pellets, dark leafy greens such as organic romaine or Spring mix, plenty of fresh bottled Spring water. You can give her treats of freshly washed carrot tops. And with new babies, make sure her environment is free of dust, excessive heat, flies, soiled towels. A fan is nice for her, just don't put it on high. Keep everything fresh and super clean. She also needs a great deal of peace and quiet. If your weather is warm, freeze a plastic water bottle so she can lay against it. Just make sure her pen stays dry.
Besides sunflower seeds, kitchen oatmeal (not whole kernels) is actually very good for boosting calorie intake of rabbits while nursing (not while still pregnant), it's easily digestible and not in any way harmful. It can be fed the kits too, from the very start. With a large litter I recommend it too, about a tablespoon a day. Sometimes I also put some drops of sunflower seed oil on it if the doe can need the calories.
I wouldn't feed much of it to rabbits that are not nursing or are not underweight due to the calories, the get fat so easily.
But I use it if I need to get simethicone or other medicine into them.
That "NO Grains!" Meme is just that, a meme.
It does not harm the kidneys, where have you heard that? If the rabbit doesn't drink enough that is a problem of its own (often because bottles are used), no matter which dry food is fed (hay, pellets, etc.). When they drink not eneugh even from a bowl there are some things to try, like a little apple cider vingar in the water, wetting greens etc.
Timothy is just one single species of grass, not those dozens and hundreds of grasses, weeds and herbs rabbits evolved with. I'm actually surprised that they live well on such a narrow diet, I guess all sweetgrasses are pretty similiar anyway and modern technologiy makes it possible to put anything else they need in good pellets.
I reckon single spiecies hay is easy to farm, is convinient and effective food, since much less gets wasted.
It's one way to feed rabbits the way you said, but it's far from being the only way, or always the best in every situation. More important is to make no big changes to the rabbits diet. The kits can eat whatever the doe gets when they start on solids.