How flattering, she really trusts and admires your skill!
To me, shabby chic is fabrics that look washed many, many times, faded and soft. They often use lace, roses, florals, pastels, ruffles. Rather better for girls than boys, but for the males you could focus on the faded look that one gets with 1930s reproductions. Many 30s prints have doggies, kittens, rodeos, and other figures that would work for boys.
I love the shabby chic look in quilts; they remind me of napping on Grandma's sun porch.
Jan in VA