RE: Best gun for kids!
Do you handload? If you do, I'd say there is no better bore for starters than the .264 and no better cartridge than the 6.5 X 55.....IF YOU HANDLOAD.
You can load the 6.5 Swede cartridge down to fairly small pellets for varmints, and the twist on the Swede and the cartridge capacity will easily handle 160 grain bullets with plenty of velocity for reaching out and killing fairly large game at significant distances. This would make the 6.5 cartridge a lifetime purchase instead of a stepping stone rifle. You may have to start with a cut-down stock though for a 9 yr old.