At 9U/10U 2B backing up a catcher's throw 9 out of 10 times ends up with them being about 5 feet in back of the bag in my experience (my kid plays on a 9U team..and no I don't coach )..they just aren't fast enough to get far enough away for the backup to be useful. Better off just having the CF come in 5 or 6 steps to backup the throw IMO. I would have the 2nd baseman move towards the bag such that they can retrieve any ball that is deflected back towards 2nd base. Agree with everything else.
This is how DD's coach does it, exactly for those reasons.