I think that 4 years old is a little young for a kid to actually have a gun in their hands while hunting. I can remember going out with my Gpa when i was that young. But i wasn't carrying a firearm. By five i was shooting .410's and .22's and squirrel hunting by age 6. I killed my first deer at age 10. I was hunting on my own by age 13. I think it really depends on the individual as to how fast they progress. Some kids are more comfortable than others being alone in the woods by themselves at that age.

Going back to the original point, I don't think a 4 year old has the understanding of what is going on as far as shot placement and decision making to be hunting deer. Small game maybe, depending on the individual.