They should have been eating grain sence 3 weeks old-4 weeks old. I wait till 9 weeks old to start weaning so at 10 weeks old they are full off mom and can go to new homes. I even do it for the ones I keep. I feel it helps them grow better.
They will always act like they don't have enough grain. Lol. You will want to cut out all alfalfa. Alfalfa hay will make them still produce milk. If they are dairy goats you can wean kids off and keep milk till about 1-2 months before kidding.