Oh, and FYI, they won't charge you when your time expires. This is from their FAQ page:
What happens when the three months of FREE Two-Day Shipping with
Amazon Prime end--will I be charged?
No, you will not be charged anything. If you earned additional months of free shipping benefits by spending in the Baby Store, then your free shipping benefits will be extended by the appropriate amount. If you did not earn additional months, then the free shipping benefit will simply end. You can always join Amazon Prime at the normal subscription price.