The new Remlins are about the poorest choice a buyer today can make IMHO.
Someone wanting a Marlin 336 woud be a world better off by buying an good condition older (preferably pre-safety) model.
And, NO, the .35 Rem isn't a chambering many 9 year olds can handle, unless they happen to be 5' 10" & 175lbs.
IMO, any 9 y.o. started with one will soon quit shooting for good.
A much better choice would be a peep-sighted .357 Rem Mag levergun or perhaps something like a .250 Savage bolt or lever (a pump might be to heavy).