First, there is no second parent for the OP's scenario. There is still a rider swap option, but that won't work for the OP because there is no second adult.
Since WDW allows children 7+ to be in the queue without an adult, suggesting using accessible access because the parent chooses not to have kids alone in the queue is quite outrageous, isn't it? What if I didn't feel safe in the queue? Should I get access as well? (No guarantee that access would be any faster, could be longer using the accessible queue, and the too small child still would not be allowed, BTW)