I also have a 12 and a 20.....the 12 primarily for my use.....the 20 primarily for my son to use.
I could take either, but the 12 is my gun of choice.
I have complete confidence in the 12's accuracy and especially it's knock down power.
I really haven't seen what the 20 is capable of in the field. If so, my opinion might change.
Eventhough I have shot the 20 on occassion at the range,
I still prefer the fit and feel of the 12 gauge which for me seems to translate into better accuracy.
One day I might not want to carry that heavy 12 around and may very well switch to the 20.
Let the kid carry that canon around. But for now it's not really an issue.