Personalized I'm Seven Years Old with Dog and Mouse Toddler Long Sleeve T-Shirt. 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 Seven Years Old with Dog and Mouse Toddler Long Sleeve Tee - Light Blue, perfect for young readers, helpers, and great friends on their birthday. A classic for Fall, Winter and Spring, these long sleeve toddler t-shirts are sure to be a staple in your child's wardrobe. Whether layered or alone, this t-shirt is soft yet durable enough to stand up to your toddler's playtime demands.