Once in a while and if we have to order for home delivery at times when it's raining too hard and we can't go out to buy at the grocery. The only resort we have is to order from fast food chains.
Only if there's something to celebrate. I try to raise my children like how we are raised and eating fast food meals were our way of indulgence.
No more than once a week, less if you can manage it. Kids should never get used to eating it as much as possible.
Only if there's an occasion like birthday parties. We train them to eat homecooked meals.
Once a week, after church. Other days its all home-cooked, healthy meals for them.