Three things to do now that are basically obvious:
1 Discuss all this with your wife.
2 Do an analysis of your monthly spending. What got spent on what, where, and why?
3 Keep a food diary for everyone, for everything that gets eaten - what was eaten, where it came from (i.e. if a restaurant, name it, if fast food takeout, name it, if fast food delivered to house, name it, if food actually cooked at home, say so. Once you have some data, figure out why all those meals that were not home-cooked were not home-cooked - why were you at a restaurant, getting takeout, etc.
Just for background, I commuted an hour each way to work when DD was young, and I still managed to get a home-cooked dinner on the table every night, to have a home-made breakfast for us every morning, and to pack her and me a lunch. DH hated packed lunch, ate lunch at work. For me slacking off was picking up a barbecue chicken on the way home from work - I still cooked everything else. So while your wife is a SAHM, and when she does go back to work, there is no reason why one or preferably both of you can't be handling meals better.
One caveat - at this point your kids are used to all this fast food and restaurant eating, they may well be resistant to shifting to eating at home. Too bad, so sad, you trained them, now you have to get them to adjust expectations. Try to frame it positively, all changes for the better are easier to make than changes for the worse. So don't say, Mommy and Daddy are broke and have to stop spending, go for Mommy and Daddy are tired of restaurant meals that taste so-so* and aren't good for us, we are going to start making our own wonderful food. And if they have friends whose parents make food they like, get recipe ideas from those parents!
*Most of us on here find that we prefer eating our own cooking, most restaurant meals are not as tasty, or they charge high prices for things we can make just as easily at home.
And maybe go over to the Case Studies Group and post your details there?