I have always used polyester batting (mostly from Joann's) on quilts while living overseas in the tropics-never had problems with it shrinking or ruining the quilts when washed. I have also had to "smooth", not stretch, on occasion when trying to squeeze every inch out of it (had no place to buy it there) and found no problems. I'm sure your quilts will turn out fine and your lucky GK's and GGK's will love them!! Lets see pics of what you have done!!!! (please)
I might add, since I have been back in the U.S., I have used Warm and Natural and although I love the feel and "evenness" of it, it is a bit hard to hand-quilt, which is what I usually do.