Re: Am I being unreasonable? My 11 daughter thinks I am!
As long as she's not a brand new driver, I think it's probably fine. These are 11 yr olds, not the driver's best friends. Generally speaking, I would think that an 18 yr old (and remember, at 18, she is an adult) is certainly responsible enough to handle driving two 11 yr olds to a science fair.
Of course I let my now 17 yr old do her learner's permit driving with her young toddler siblings in the car...yeah I was there in the passenger seat, but she was the driver.