Buon appetito/Andiamo a tavola
Obviously mine is not a literal translation, but if your exclamation is to be used when you are sitting at the table, as a signal for people to start eating, then Buon Appetito is the thing to say. English does not have an exclamation to translate Buon Appetito (Bon Appetit in French) and so sometimes people say "enjoy", "let's eat".
If you are sitting up and you want to invite your guests to sit down at the table for the meal, then you can say "andiamo a tavola" or "andiamo a mangiare".
This is are deceivingly simple expressions which have to take into account a lot of non verbal clues and context.