Could this also be translated "You are ours tomorrow"? I was envisioning talking to that "Doggie in the window" whom we are about to adopt....
"Siete il nostro, domani" with a comma, could be what you say, but without context, no way, nobody would ever say it.
Furthermore, "VOI siete il nostrO" don't agree, without context, it's a strict NO.
That would be for a bunch of dogs, not a single puppy! Speaker and what is spoken about are different!
Probably the same as in English: "You are our tomorrow" and "You are our future" might mean the same but not necessarily. Speaker's preference...
OK, someone mentioned a graduation ceremony, but, as someone who pays attention to non-profit public interest groups, I hope people will look at children that way every day. It might be said in church, a classroom, or simply at a dinner table or pep talk.... The PIRGs set up a youth oriented program for renewable energy activism, for one....Certainly the Unitarian Universalists have a Sunday school program as well, for another kind.