Hi there. Another big spender here (compared to many in this forum, but small spender compared to my colleagues). I won't say how much we spend monthly, though. You are braver than I.
Some ideas for incremental change instead of cold turkey on various things:
1. Use credit card points to buy gift cards to use for special dinners out and other entertainment expenses. Since you already pay the au pair to provide child care, this can make those date nights feel 'free' without cutting them entirely.
2. If your kids are really picky with food, work your way slowly from the fruit pouches to whole fruit. For example: Start with the make-your-own pouches. Start making applesauce at home (super easy) to use in said pouches. Move on to offering applesauce to kids at home in bowls. Make the applesauce more and more chunky. Start serving chopped apples in bowls. Move to home-sliced apple sticks, then apple slices, then *ta-da* whole apples. This can be done over a month and without too much difficulty or upset from anyone. Add in clementines, which most kids love. And grapes, etc. Now your kids are eating real fruit! (If your kids aren't that picky, go right for grapes, which are essentially bags of sugar anyway.) If your kids are used to getting snack bag sized treats of, say, veggie straws, move to getting the big bag and portioning them out into ziplocs. Then cut back slowly on the veggie straws b/c they're really not great (ahem, speaking to myself here).
3. Cut any expenses that are purely your own to control rather than imposing limits on others in your household first. Do you buy a lot of books on Amazon? Start visiting the library for your own reading. Take the kids with--they'll love it (most kids love the library), and maybe your spouse will join one day, too. Offer to take over the laundry and start line-drying. Manage the thermostat yourself. Start doing your own pest control and minor home repairs (consult youtube). Buy your own clothes at Goodwill (then add in the kids' clothes). Small savings percentage-wise, but your spouse might appreciate your extra efforts with the kids and the house and limiting your personal spending and you will have a bit of a mind-shift. You will also sound like less of a scold than if you try to tell her to do these things herself while doing nothing yourself.
4. Definitely don't start limiting your current au pair's benefits, but if you switch up the au pair (if the contract ends) then consider being less generous with the car for the next one (60 mile trips three times a week is a lot). And use all the hours of au pair time you are allotted. My friends who have au pairs or who were au pairs have said that "light housekeeping" was expected, which included doing the kids' laundry and keeping the kitchen clean. Especially for families where both parents work and the kids are school-age and the au pair's time will not be exhausted during the day just on childcare. Other friends use the time for night time babysitting for their date nights.
5. Talk to your spouse now about whether she would be open to moving to a smaller house once the kids are in school and you no longer "need" the extra bedroom for the au pair (a debatable point, as I've been told by friends that it's easier to keep the au pair than arrange for aftercare and pickups when both parents have work hours that end after 6pm). It's worth testing those waters. You might mention that you could cash in on your equity at that point by moving to a smaller (cheaper) house and pad your investments to make your FI date come sooner. Smaller house usually equals smaller RE taxes and HOI as well as a smaller mortgage. Maybe you could find a smaller house that is "done" and needs less renovating??
6. Ask your kids if they enjoy the activities that they are in. If they are, fine, maybe keep them. If they are not, consider dropping one or several. I made the mistake of thinking that my kids should try every activity offered at their montessori. One year I spent over $4,000 on my older two because they were in (oh, I'm embarrassed to list them all but here goes): French, Mandarin, basketball, soccer, karate, piano lessons, swimming, and dance (for the younger) and Spanish (for the older). For the record, neither of them learned swimming that summer--we had to do that separately again later. Neither of them remembers any of the French or Mandarin (except some of the French alphabet and how to say hello and thank you in Mandarin--which they probably learned from Ni Hao Kai Lan).
7. Give your spouse monthly reports on household spending without judgment. "We spent $11,000 this past month." Next month (after you do some of your own cutting, "We spent $10,500 this month--down $500 from last month!" Start to get her used to thinking of how much money goes out each month. It's easy to ignore the total and only think of the one "extra" item we bought for ourselves, and she might be doing that and thinking "but I don't spend anything, it's not in my control." Maybe she'll ask for the breakdown, maybe not. Giving her the monthly report is a way to bring reality to her without making a big deal of it or laying blame.
I will say that I relate in one way: my spouse (though quite thrifty) has very little interest in FIRE. That's all me. So it's hard to convince him to limit his spending to achieve a goal that is not his. But when I make the effort to control my own spending without telling him he should spend less at Home Depot, he seems to follow suit. When I make the effort to say "you know, let's eat in tonight instead of ordering out--how about I make XYZ"--he is more likely to say yes than if I say "what should we do for dinner tonight?" Or if I frame it in terms of health: "You know, I find I eat better and I eat less when we eat at home--let's not get chinese this weekend--will you make your delicious homemade egg-fried rice?"