If you're flying to the U.S. then, yes, your baby needs a valid passport. This applies even if your baby is only flying through the United States while on route to a different destination. However, if you are crossing into the U.S. by land or by boat then you can use either a passport or a birth certificate for your baby. Be warned that it is up to the border guard's discretion to let your baby cross the border if you are not using a passport for your baby. If you have a question about passport requirements look at the Canada Border Services Agency website for additional information.