Since the best time to go to Belize is almost any time of year (even the rainy season is still pleasantly warm, and doesn't prevent you from enjoying aquatic activities), your biggest concern will be gaining entry into the country.
To enter Belize, you must have proof of onward or return travel (such as a plane ticket). You must also have proof of sufficient travel funds, although this is rarely checked. Travelers who plan to go to Belize for purposes other than tourism, or those who want to stay longer than 30 days, must obtain a visa.
If you want to stay longer than 30 days for tourism and are already in the country, you can request a one-month extension from a Belize Immigration Office, which are scattered across the country. Another option is to simply cross the border into another country and then return into Belize with a stamp that’s good for another 30 days.
Do note that if you’re traveling with small children, you may be asked by officials to show birth certificates for each child.
With your entry granted, it's time to explore the country, and you'll have plenty of options for getting around Belize. Keep in mind that whether you exit the country by air or land, you will have to pay a departure tax in Belize.