A married couple with 2 kids would pay $54,950 in federal tax and $18,900 state tax on 250k income. Effective tax brackets 22%/7.6%.
While I’m sure that there are daycare centers that cost $1k and even $2k/month/kid, you can find perfectly good family day care for your kids for $700/month/kid on Craigslist. For which you can pay with pre-tax money using your 125 plan. And you need expensive full-time day care till they are approximately 5 years old.