The Marlin 39, and Rem 121 would be my choices for quality and accuracy. That said, they are both man sized .22's. I don't consider either one sized for a kid.
My 1958 production Rem 121 is a tremendous .22, loads of fun and very accurate for open sights.
In regards to the Marlin 39A rifles, a Mounty model might be a tad handier for kid. But LOP would still be an issue.
