I would just find a cheep factory stock, buy a slip over limsaver recoil pad and cut it to whatever length you seam appropriate currently.
You can pull the slip on pad off in the future and glue a spacer back into the stock if you need and then just slip the pad back on.
Most cost effective way I know to let a rifle grow with a kid.
Once they are finished growing just replace with the original factory stock or custom aftermarket and correct LOP
