We took our 5 month old and two year old on a Mexican Riveria cruise( years ago) . They were perfectly fine without any "extra " immunizations( they had their regular ones) You are only in a port for 6 to 8 hours, you most likely will not be in much contact with local children, your kids are more likely to get a cold form someone on the ship or on the plane coming over. Don't worry about it. We didn't eat or drink anything local, I brought a couple of juice boxes for my 2 year old and some snacks from the ship. The baby was breastfed. Have lots of fun!!