James,
Both Ambergris Caye and Placencia have international schools that are managed by expats who want the best possible education for their children. The Island Academy on Ambergris Caye has been in existence for quite a few years. Lady Dixie Bowen is the head mistress. It is a very active school and most of the teachers are North Americans.
The Peninsula International Academy is a private school in Placencia that was started by expats a few years ago.
There are also some good Catholic and Anglican run schools on the mainland, in Belize City. That is where many wealthier Belizeans send their children for high school. But your daughter is young and I assume you want to live somewhere where your daughter can attend school close by. Check out Placencia and Ambergris Caye. Placencia is lower key and less populated. There is a lot to do on Ambergris Caye, but it is not as quiet and low key as Placencia. The cost of living in both places is about the same. There are also quite a few young expats with families who have moved to Placencia, so you would find quite a few expats from around the world who have young families living in Placencia.