Expressing present with future progressive

Question

It’s 3P.M. I have get off my car and on entering our house I see my wife Jane and ask her: Where are the kids? She answers: They will be playing football the whole afternoon. From her answer I’m drawing the following inference. The kids are playing football now, and that they will be playing football till the end of the afternoon.

Can one use future progressive (continuous) tense to express future action commenced before the moment of utterance of the above dialogue? If not, the cumbersome construction must be used
She answers: They are playing football [now]. And They will be playing football the whole afternoon.

Answer 1

My short answer is yes, you can. Both of your imaginary Jane's answers seem fine. "They'll be {doing x activity} for {x time period}" would mean to me that the 'they' in question have already started that activity. The only thing I would take issue with in your post is that we would more typically say "I get out of my car".

Answer 2

Your wife hasn't answered your question directly. Instead she's given you a clue that you can use to infer the answer to your question. She's told you where they will be and you are allowed to deduce from that where they are.

This is quite common in conversation.

Where are the kids?

There's a special deal on at the cinema.

Again the "answer" doesn't answer the question, but from it you can infer where the kids are.

So "will be playing" doesn't mean "they started playing earlier". It doesn't explicitly say anything about earlier. But you are allowed to deduce that from context.