My outdoor play cut off is -20 but I would think for a 10 minute walk I would likely up it to about -23 to -25? What is this parent planning on doing when the child goes to school and has to go out for recess? I would make sure the child is almost fully covered and it should be fine.

Where are you located and what is a "normal" temp for you? This winter has been brutal...we have stayed in A LOT!!