It never hurts to ask, and it's certainly not the most extreme request ever.

But, with all due respect, I agree with most of the posters here. Whether we're talking about doubling up in a room or breakfast coupons, from a hotel's point of view there's certainly a big difference between "bring the kids along" versus "bring your buddies/in-laws/relatives, etc. along".

In the case of the "bring the kids", the bottom line is likely to be revenue the hotel wouldn't have gotten otherwise. Certainly that could conceivably also be the case with "bring your buddies"....but it's more likely that the hotel is losing revenue by not having the second couple pay for their own food and lodging.