I have made several t-shirt quilts, especially for high school grads. Using a fusible interfacing is key--but watch out when applying an iron around silk screened logos--they can melt. I have done plain squares, and fancier pieced blocks which used the t-shirt piece as the center (log cabin variations, square-in-a-square etc). It's also fun to select fabrics for your borders and sashings which have some significance to the person receiving the quilt....like sports or music themes or in your case baby items. Hint for shirts which have the logos printed too high on the chest to make it the center of a square, piece on part of the lower shirt above the logo, then cut to your selected size (kind of like splicing in a short piece of wallpaper). Once it's quilted you'll never see the seam. Above all, have fun, and enjoy making the memories of your grandchild!