I bought some printer t-shirt transfers and some white shirts, designed it on PSE 6, adjusted the saturation a bit so the colors would be bright, printed, ironed and ta-da!
I used Kristin CB's All About Her for Chloe's shirt, Traci Reed's With Sugar for my cupcake-loving Emma, and Julie Billingsley's Revolution for Aidan's. I am thinking of getting a glitter pen and decorate them even more.