I bought my 10 year old a Mossberg Mini bantam youth 20 ga, cutest little gun in the world. but to be honest its a wolf in sheeps clothing. So small and light that it can jump outta your hands and punch your face! Er well it stayed in our hands but the punch was real, I used it to fill my first tag this year and it was a fun little gun but not for little kids or first timers, My son now uses my Remington 870 youth 20 ga and is much happier.. I get some grief from friends for using a 20 but I've killed 10 or so birds with little guns and its more rewarding and frankly a little harder than smacking them at 50 yards..
Don't make the mistake i did and let a kid shoot something too big for them...it took my boy a while to get over the punch. All is well now but he was very gun shy for a bit. Also if your gonna kill a turkey at 15-20 yards you don't need a full or a turkey choke, a modified will work and reduce a lot of recoil. 30-35 will require the full.