Actually, it's not. The Riders conditions talk about unaccompanied minors, but the Drivers conditions do not.
In South Australia the driver is required to be accredited. One of the prerequisites to accreditation is a Working With Children Clearance. My Driver Accreditation Card has this endorsement printed on it, "Driver cleared to transport children".
Looks pretty clear to me ... here ill show you ... and the T&C's are Uber's not the law in your local province state or country.
It all comes down to insurance and when it goes wrong that is who really has your back your insurer. Uber's insurance policy will cover the passenger not you and as such they have there T&C's there to show that they have been responsible and therefore wont be liable If the Third party (the contractor/Driver) or the Passenger break there T&C's for the service. Simply put if you allow the passengers to break the T&C's you are now taking responsibility for everything. You can do that but if you do and you want to do more for your customer such as transporting a minor it is all on you not Uber. BTW if you break the law your the insurer wont pay.
So for your peace of mind why don't you call your insurer or email them and ask them if they will cover you for any scenario you can think of (in this case public liability). I did and changed my insurance from NRMA to a commercial policy from Alliance that is designed for Uber drivers. In QLD our CTP is set to change soon and we as Ride Share Drivers will have to pay for a better CTP insurance.
So yes you can transport a minor but you are responsible not Uber.