Most definitely a copperhead. I have considerable experience with these taxa. I can tell at a moment's glance the difference between an Agkistrodon and a colubrid. The way you are taught to key out the difference is the "V" or "Y" patch eastern corn snakes have on their necks, which the copperhead is lacking. But to someone like myself, who has seen literally hundreds of these animals, the triangle shaped head, body look and color/patterns of the copperhead is instantly unmistakable.
Mailing a snake is fun! Tho not allowed by by postal service or UPS. But many folks still do without telling. Airplane freight companies, like Delta Dash, just ship such animals for zoos and longstanding commerical accounts nowadays.
I used to send salamanders very successfully thru the mail in winter - just put'em in a gallon plastic jug with a bit of water. Tho that was for collectors who wanted them as pets - it is really not good habitat husbandry to release a species from one geolocation to another, even if the same species occurs in both areas.
Yes, with kids around it the best thing for most folks is to kill the venomous animals. Herpetologist friends of mine, being more concerned with the animals than the average parent, would never kill the snakes, but teach and discipline thier kids, while maintaining ever constant vigilance. And do the occasional (local) relocating.
