If you look at the room descriptions on the Four Seasons website (click guest rooms on the left toolbar when viewing the San Francisco location) it gives a description including maximum occupancy for each room type. San Francisco does indeed force you into an Executive Suite with 2 adults and 2 children.

I do notice than Four Seasons tends to force families to book higher room categories, although it is a bit rarer for you to be forced into an Executive Suite. But if you check other locations you will find the lowest room categories saying they can't accomodate a family of 4, while higher room categories (which in many cases are the same rooms, just with better views or on higher floors) will accomodate a family of 4.

I agree with you - it is definitiely unique to Four Seasons. I have stayed at many Ritz Carltons and other than some hotels imposing extra person charges on the club level for more than 2 people (even kids) in a club room, I have not seen a Ritz that won't allow 2 adults and 2 kids in a double bedded room.