Effective tax rate would come out to about $100k, not 180. Income tax brackets are marginal... https://www.taxact.com/tools/tax-bracket-calculator.asp and https://smartasset.com/taxes/california-tax-calculator#CZ1Kw...
You also just kinda snuck in a random 72k/year for something that was never discussed.
How about a spouse who also works? Would likely cover that 72k right there. 300k was a single person's income in the context above.
How about public school? How about just not sending them to the most expensive private schools possible?