Hi Brandon, There are two ways to get to San Pedro - by boat or by plane. There are more than one options for either way. You can either use Tropic Air or Maya Island Air to fly directly from International Airport to San Pedro, which is the quickest and, in my own view, the most pleasant way to travel. It's certainly not the most inexpensive. I prefer Tropic Air to Maya Island Air based on my experiences with both. The next price down would be catching a taxi from International Airport to Municipal Airport and flying from there. That would save you considerably with a group of 4 adults and one baby. Some discounts on flying can be found through Tacogirl.com
By boat there are three options. There is a private ferry directly from the International Airport but someone else will have to give you up to date information on that service as it has changed a lot in the last year and I have no idea if it's even operating at all. If it is, I have no info. The least expensive option are the two public ferry services, which are Ocean Ferry and Belize San Pedro Express. My personal preference is Belize San Pedro Express as I particularly find their dock pleasant and safe. You would have to catch a taxi from International Airport to one or the other ferry services which are both in the same part of town.
Keep in mind that the time of your flight arrival into Belize may determine which mode of transport you will have to take as the last ferries are at 5.30pm, while Tropic Air will run flights to ensure you get to San Pedro from International, whenever you arrive as long as you have booked in advance.
You'd need to be more specific about your budget and desired amenities before anyone could pipe in on accommodation as there is tons of it.