My cutoff is -20 temp or windchill. If the temp is -15 and it says -20 with wind I will go check first to see how windy it is, if not too bad we will go out (my place is windy)!. We have been in all week as well. I have one parent who sometimes comments about us not going out even though it is past -20. She says " it doesn't seem bad" - of course not when you are going from your house to your car to my house. Try playing outside for 30 minutes! Good grief lol.
Personally I think -10 is still warm enough to be going out. Yes its lots of work to get everyone dressed but kids need fresh air as often as they can.