they will start with hay - and its good for their digestion, as the stomach arrangements in goat kids develop over time.
they'll then help themselves to whatever hard feed & vegetation mum has when they are ready, and still take milk from her ... in my experience, for as long as she'll let them!
once they are ready to move on to a new home, send some of "your" feed with them, & tell the new owners exactly what it is, as changes on food need to be Slooooowww! in goats
h.t.h