I am taking my wife back to Belize for our second time at the end of May for our 10 year anniversary. I would like to have our best friends come down with our kids (2 girls - ages 5 and 6) AFTER we are already 2-3 days in to our vacation. This will be a total surprise for my wife. I have a few questions now that you have some background information:

1. Do my 2 children need a passport to travel to belize?
2. Will there be any issues with our best friends flying with our 2 children to belize?
3. Any other possible problem or issues you can see with this?

Thanks for your answers / feedback in advance!