Traffic laws will vary by state. Even for school buses.
But to answer your question, in my school district, given those circumstances, no you would not have to stop. But California is a different animal than most.
Again, it depends on the vehicle code for your state. And in Illinois, the Vehicle Code states:
(625 ILCS 5/11‑1414) (from Ch. 95 1/2, par. 11‑1414)
(Text of Section from P.A. 93‑180)
Sec. 11‑1414. Approaching, overtaking, and passing school bus.
(a) The driver of a vehicle shall stop such vehicle before meeting or overtaking, from either direction, any school bus stopped at any location for the purpose of receiving or discharging pupils. Such stop is required before reaching the school bus when there is in operation on the school bus the visual signals as specified in Sections 12‑803 and 12‑805 of this Code. The driver of the vehicle shall not proceed until the school bus resumes motion or the driver of the vehicle is signaled by the school bus driver to proceed or the visual signals are no longer actuated.
(b) The stop signal arm required by Section 12‑803 of this Code shall be extended after the school bus has come to a complete stop for the purpose of loading or discharging pupils and shall be closed before the school bus is placed in motion again. The stop signal arm shall not be extended at any other time.
(c) The alternately flashing red signal lamps of an 8‑lamp flashing signal system required by Section 12‑805 of this Code shall be actuated after the school bus has come to a complete stop for the purpose of loading or discharging pupils and shall be turned off before the school bus is placed in motion again. The red signal lamps shall not be actuated at any other time except as provided in paragraph (d) of this Section.
(d) The alternately flashing amber signal lamps of an 8‑lamp flashing signal system required by Section 12‑805 of this Code shall be actuated continuously during not less than the last 100 feet traveled by the school bus before stopping for the purpose of loading or discharging pupils within an urban area and during not less than the last 200 feet traveled by the school bus outside an urban area. The amber signal lamps shall remain actuated until the school bus is stopped. The amber signal lamps shall not be actuated at any other time.
(e) The driver of a vehicle upon a highway having 4 or more lanes which permits at least 2 lanes of traffic to travel in opposite directions need not stop such vehicle upon meeting a school bus which is stopped in the opposing roadway; and need not stop such vehicle when driving upon a controlled access highway when passing a school bus traveling in either direction that is stopped in a loading zone adjacent to the surfaced or improved part of the controlled access highway where pedestrians are not permitted to cross.