Personalized I'm Six Years Old with Dog and Mouse Infant Romper. Celebrate your birthday with Dog and Mouse, the unlikely best friends from the children's book "Dog and Mouse" by Michelle Nelson-Schmidt. I'm Six Years Old with Dog and Mouse Infant Romper - Raspberry, perfect for young readers, helpers, and great friends on their birthday. 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)