This is my 3rd year teaching primary and it is a complete No-no to have one teacher in a classroom of more than 10 kids when there are kids under 5 years old. If I was put in that position, I would either drag one of the parents or Primary Presidencies in there or drag the kids out of the classroom and move them to where the Presidency was meeting. By the way, I wouldn't assume that the Primary Presidency was just chatting away. They do have to plan and such and a lot of times, Sunday School is the only time the presidency can get together to do that.
As for support, if I don't get what I need from the presidency for a lesson plan, I wouldn't go to the bishopric. I will go ahead and revise the lesson.
The only time I would get a bishopric involved is if the issue is regarding the health and safety of the children or if it is a matter of the children getting taught false doctrine.
Hope this helps.