The only dress code is wear whatever you are happy to see in your pictures for the rest of eternity. For me that means i make sure my ****s are covered by my shirt (even with funky camera angles.) People never check this then are shocked when they get an eyefull in every picture.
Shorts and polos are what the whole family usually wears. But that is often our normal at home as well.
As long as you have clothes on and not your swimsuit it will be fine.