It costs about $3.5k/month to rent a two bed in the Bay Area, $1.2k/month per kid for the day care. Add in $1.2k for grocery, utlities, insurance, gas, car maintenance ..etc, and you are looking at around $7k a month with two kids. It would be closer to $9k with entertainment/vacation/car payments.

You are right that someone with 450k gross should be able to comfortably handle this. It is different story for the majority that make 250k or less.