What makes this your child's dream trip? (that could help guide us).
If you like hiking and beaches, Id' suggest taking one of your SF days to drive the GG bridge, then the headlands and Highway 1 to Muir Woods for some tall trees (make a reservation ahead for parking) and finish at Stinson Beach with a picnic dinner from Parkside followed by the sunset.. It's a northern CA sand castle/surfing/picnic beach, not a swimming one (cold water), so you don't need shorts or bathing suits.