4) threaten that if they do not stop at at least one marker at some point on the way down you will make them wear those ridiculous ear / antennae things attached to their helmet (also have very competitive boy aged 9!)

Ok so i did lose my son(9) on the sloes but just thought i would share tips on how to get him / her back to you safely.
1)make sure they have your mobile number in their jacket pocket and know its there.
2) then depending on their age agree where to meet if they go too far ahead - possibly at the chair lift / ski hire shop.
3) agree to stop at each marker on th slopes to check all are present and correct - this won't work if you have competitive kids who are racing down the mountain and there is a prize or pride involved... oh well that's boys for you...

Also just wanted to add that my sons dark jacket didn't help - so if you can get them to wear a bright jacket which will make them easier to pick out on busy slopes.