Single Shot 12 gauge typically will have more recoil simply because the guns weighs so "little" in relation to payload . Rule of 96 if you will.
MY recommendation for Single shot shotgun have always been 20 gauge and smaller, just for this reason, especially in Youth sizes.
28 gauge is just flat THE ticket and gets the most grins, smiles and happy-dances.
Recoil complaints on the 20 are valid, still IMO/IME the reason some say the 12 is "less to them" over a 12, is (a) gun fit ((b) correct mounting and basics of shooting.
12 ga - folks will "think" as "this light gun with them loads are going to hurt"
So, they correctly mount gun to face and use proper technique.
20 ga - folks get Complacent. "Just a yellow shell, this won't hurt" and Improperly just toss the gun up and shoot.
Makes a difference...
30-30 in these Configs are popular here.
Lady I have known forever uses one for Deer Hunting.
At first the recoil "bugged her".
So I got her involved in shooting some skeet, to assist with bird hunting.
She picked up on shotgunning real fast. Gun Fit and Correct Basics and "duh, my gun does not fit".
So we fit her Single Shots, including the one with the 30-30 set up , Pach Decel, and raised the comb, and she does NOT have a problem with recoil.
She likes these Single Shots, accomplished shooter, hunter and all.
From learning gun fit, she got her Win 94 fitted, with a Pach Decel.
Gun fit , Pach Decel, Correct Basics - makes one a better shooter - Mentors
Oh, she has one single shot 30-30 set up with scope, the other iron sights.
Funny, but true.
Goofing off, not being serious she shoots a running Spike Buck, with the iron sighted 30-30 single shot.
Gets this deer in and checked.
Comes back to just shoot the breeze and goof off...toting a single shot shotgun, with the idea she "might" take some small game (rabbit , squirrels) with this shotgun or .22 pistol (hand gun hunter too).
She is carrying some 20 ga slugs. "Just because" and "what one does".
Sneezing Fit. I mean she gets to sneezing! Blowing her nose with a gray bandanna, and Sneezing. Finally...stops and put up this bandanna and this HUGE Buck, crashes through from the thicket and running full bore 20 steps lateral to her in this "less thick" area.
One 20 bore slug on the run from a plain bone stock, single shot H&R Topper with bead sight.
Check in place : "You back again- so soon?"
Of course we tease her:
"We have
got to record that sneezing fit and nose blowing , we will make a fortune with a Buck Call".
Neat guns these all are -proven and still proving.