while i agree with prior poster that garden grocer is a great way of doing this, and actually what i do when i go, if they want to send a package ahead, it is easy to do..
simply find the address of the resort where they are staying, (allears.net lists every address), and address package to themselves, add the address of the resort and the date of their arrival. no matter when they send it, bell services will keep it for them. when they arrive simply ask for it.
i learned the beauty of garden grocer the first time we took my grandchild, who was then 10 months old. our next trip will include grandkids who will be 3, 2, and 3 months old at the time. diapers are bulky to ship or carry, formula is heavy, and wipes are heavy, heavy = more expensive to ship. but the major advantage is that we have fresh foods and dairy for them. things like fruit, yogurt for breakfast, and MILK, MILK, MILK, you should see what those kids can go through. either way, taking a baby and it's supplies should be no big deal, don't let them stress you in any way