So take a look at the SS calculations again. They take the average of 40 years of earnings, so if you don't work for 3/4 of those, your benefits take a huge hit. I ran a super-quick calculator that assumed you had earned $70K/yr since you were 18-19 (so for 15 years before retiring at 34), and I got $1100/mo. for you. Obviously that will be higher/lower depending on how long you worked and your earning history, and you are right that your wife will get half your benefit; but also remember that when one of you dies, you drop down to only your SS again. I'm glad you did the math without considering SS, but it's worth getting a solid sense of what that is, because that is your "things hit the shitter after I'm too old to work any more" backstop.
Also going to beat the dead horse over kid expenses. Obviously, you don't have to sign your kid up for gymnastics lessons or let them play in the school band or go on field trips. But the real question is are you -- or your wife -- going to want to offer them those advantages? If all the kids in the neighborhood are playing rec soccer (our neighborhood rec league is about $100 per kid per sport, not counting equipment costs), will you be happy telling your kids they can't? What about school supplies and field trips and tickets to the school dances and all that? We spend hundreds of dollars a year just on those basic public school "extras" -- and if we had to rent an instrument for my kid to play in the band, that would be a lot more. What are your college plans? Don't assume your kids will get full rides anywhere if you are not employed; a lot of schools will assume you can afford to pay a cut of what you have saved, too. So do you plan for them to take out loans? And do you have a sense of the magnitude of what those loans will be, and how long it will take them to pay them back?
I agree with everyone else here that you need to take a much closer look at what you want your life to be like -- spend less time projecting SWRs and more time pinning down the details of the life you want to live. Don't assume that cheap insurance will be available and cover everything; research the cost of an ACA plan, and then look at what that plan will leave for you to cover out of your own pocket. Think of the kind of activities you will want your kid to do -- sports, music/art, driving, etc. -- and research what those things actually cost to give yourself a baseline. Think about the kind of college option you want your kids to look at, and run a calculator to see what your expected family contribution would be assuming you are FIRE'd with the appropriate 'stache and no other income. Etc.
Yes, you can get by on $30-35K/yr. People get by on less and live perfectly happy lives doing so. Kids shop at Goodwill and don't play in the band and don't get braces and work part-time jobs for spending money/college tuition and take out loans or don't go to college at all or live at home and go to CC. The real question is, when the kids are 16 and want phones and to drive and to hang out with their friends and are talking about college and all that, will you still want to be living on $30K? Or will you and your wife want the flexibility to let them play sports or in a band, or buy the nicer eyeglasses instead of the ones on the cheap shelf, or pay the EFC at the local college? Plan your future spend around that, not around unfounded assumptions.