I assume you mean cartons of fresh milk (& not straight from the cow! ). My Mam always used to put a few cartons into the freezer at home for 'emergencies'. Once the milks defrosted, before you open the carton, shake it & the milk should be fine.
I WORK ON LIGHTHOUSES AROUND THE COAST OF IRELAND AND FREQUENTLY HAVE TO FREEZE MILK FOR UP TO THREE WEEKS.
1. SHAKE WELL BEFORE AND OCCASIONALLY DURING FREEZING,
2. ALWAYS DEFROST IN FRIDGE, OVERNIGHT.