As long as you are giving a wide variety, they will probably not overindulge in any one thing. My kits get BOSS along with their oats, barley, and beet pulp in the creep feeders as soon as they are out of the nest. I would be cautious with the kale and any brassicas, only putting as much as the doe normally eats at one time, and they will get some nibbles of it before she chows it all down. I haven't had any trouble putting a 2" chunk of carrot in with kits, and upping the amount as they grow.
One thing I did when I first started feeding greens was to always feed hay first, then grain, then greens or veggies. I have 24 holes, (plus growout pens now), so by the time I got back to the first cage fed, they had already been eating other things so weren't ravenous. If you feed the "dry matter" first and follow with the veggies in about twenty minutes, I don't think you will have any issues.