Awesome job to an awesome friend!!
I have an idea for you, depending on how much the girls like dresses, if you buy a womans tank top and some tshirt jersey you can make the cutiest grow-ing up girls dresses. Get the girls to put the tanks on, find where their hips are and then cut the tank to that length leaving enough for a hem. Measure from where you cut the tank off (being mindful of adding in the hem on both ends) to where they wear their skirts. Cut a band of fabric double the length and cut. Fold the band right sides out and sew to the bottom of the tank. You now have a self lined skirt. If the top of the tank is too low for their age group and likely under the arms as well, take the jersey and outline the tank on to it making the neck not as deep and the under arms more shallow. Cut it out, sew in the side seams and serge the edges and tack under the shoulders and under the arms. These are the fastest easy peasy dresses Ive made. You can always look for Tshirts at the GoodWill or any second hand store to cut up for the skirt part, the tanks too if you are lucky!