Personalized Happy Birthday with Dog and Mouse Infant Romper. Dog and Mouse are excited to wish you the happiest of birthdays! Happy Birthday with Dog and Mouse Infant Romper - Heather, perfect for those who love this friendly duo from "Dog and Mouse" by Michelle Nelson-Schmidt. Meet your new favorite outfit! Keep dressing simple with this one piece, lap shoulder t-romper. Super soft and perfect for baby's sensitive skin. 5.5 oz. 100% combed ringspun cotton premium jersey (CVC Colors are 60/40; Heather is 90/10 combed ringspun cotton/polyester)