I was curious what this might look like, so I ran some numbers. It would be easy to hit this in a high cost of living area where rent will easily run 5-6k per month, but what about a medium cost of living place? I assumed a family of 4 with both parents working for 75k each and a 20% total tax rate (FICA, federal, state). All of this is based on what I know of typical cost of living items in the US.

After Tax Income (monthly) 10000

Housing 2500 Child care 1500 2 Car Payments (25k each) 1000 Groceries 800 Medical (incl. insurance) 800 401k (6% deduction) 750 2 Student Loans (30k each) 700 Utilities 400 Auto Insurance 300 Total Core Expenses 8750 Leftover for Discretionary 1250

So, you'd have 1250 per month to cover clothing, auto fuel, dining out, pets, fun money, subscriptions, activities for the kids, gifts, etc. You could easily run that to zero or below every month.

Now, there may be some room to cut in this budget, like not funding your retirement and giving up your 401k match or living in a much smaller home. But I would also say some of these numbers are very generous. Rent could be over 3k, most people don't have a 25k car loan, if you own your home you can get hit with random major repair costs, and probably most parents would laugh at my estimated child care cost.

I think a key takeaway here is that kids are really expensive. Aside from the child care costs, most people with kids will want a little more living space than is doable in an apartment and kids go through food and clothes like crazy. You could probably chop at least 2-3k per month off this budget if it was a couple living in an apartment closer into the city core, with shorter commutes and maybe even options for public transit, biking, or walking.