Talk to your pediatrician about vaccines. Although the reality is he's too young vaccines such as typhoid and Hepatitis A. Back when I was still working, we sometimes gave vaccines early to kids who were going to traveling to high risk areas. These vaccines were essentially an extra dose, they didn't count in terms of coverage for school and day care.

However, your physician will know, or, should be able to find out if anything extra should be given. Make sure he's had his second set of routine vaccines.

I'd probably choose either Ambergris or Placencia. Nice places to stay, easy to get around. Lots of choices for food and drink.