Shotguns for kids

[Biscuits]

My 12 year old son wants to do clay busting.

He's tried out my over-under 12ga, but it isn't suitable for him due to too long a length of pull and too heavy. He hasn't reached the teenage growth spurt yet.

Looking for suggestions for something which isn't heavy and has a shorter length of pull. Even better if the butt has spacers so the LoP can be increased as he gets bigger.

Needs to be legal in NSW.

I'm not even sure what type of shotgun is best. Single shot is lightest, but it's only single shot. Double barrel? Lever action? Straight pull?
Also not sure if I should try to find a 20ga, or find a 12ga and use light or low recoil loads.

[No1Mk3]

O/U 20g, several nice guns around at low enough prices to be replaced in a few years as he grows. Many small frame shooters do very well with 28g guns of which there are several choices.

[womble]

Something like this https://usedguns.com.au/products/20237804?_pos=8&_sid=ef3a293f3&_ss=r&_fid=e27ac2b5a