anything in Colo. would require both of you to have passed hunter safety course, assuming that you were born on or after Jan. 1st 1949. Hunter safety courses from other states do qualify.
Your son would not be allowed to use his cross-bow during archery in Colo.
One possibility might be to look into a late season rifle doe antelope hunt here in Colo. Easy to get tags, a month to hunt/Dec. and would be easy to get permission on private land to shoot a couple of doe antelope.