Is it true that making breastmilk can help breast growth?

Yes: When your breasts are full they will be enlarged. However, the growth may or may not be sustained when you stop breast feeding. I have seen it go both ways.. Up or down.

Maybe: Pregnancy/breastfeeding trigger the increase in activity & number of milk producing glands of the breast.These may displace local fat stores as they enlarge into the area. Whether or not these remain is an individual process. Once the milk production declines these can return to pre-pregnancy size and the displaced fat may not return.