You can wear whatever you want in Placencia. You can even walk barefoot in Placencia.
Placencia is a beach town that is long but very narrow, so you are at the beach every day. People in Placencia wear a t-shirt or shorts every day and some flip-flops. It is easy to dress every morning, even for the kids. Even if you were the type of person who likes to be in fashion, you would still wind up just wearing very simple clothes.
There are many tourists who go for the beach look. They wear gorgeous dresses that are transparent enough to see the bathing suit. You can be who you are and what you want to look like in Placencia. No one will go after you. Be who you want to be in Placencia and in Belize in general.
(Pictured: typical fashion statement in Placencia.)