A phrase that children use to beg their parents for treats such as sweets (candy) or crisps (chips). Is essentially another term for a sugar craving or craving for a certain treat food. Someone who is hungry treat will refuse all savory foods and will insist that they are only hungry for treat foods.
Kid: Mum, I'm hungry.
Mum: Here have this banana.
Kid: No I can't I'm hungry treat, I can't eat a banana it has to be a treat!