April's free Game of the Month at playwithsound.com is for two players at a time, sharing a xylophone. It's based on a West African balafon playing technique and is very good for developing rhythm and co-operation skills as well as exerting a calming influence on players and others in the vicinity.
Here are five scales that can be played on most 'school' instruments. Nearly all of these come with extra keys for the notes F# and Bb intended for substitution of F and B as required. Obviously, if you have a fully chromatic xylophone you have more possibilities but I think you'll find a lot to interest you in these scales:
C Major pentatonic: CDEGAC
D Minor pentatonic: DFGACD
'Japanese' pentatonic: EFABCE
C Lydian pentatonic: CDEF#AC
E Blues pentatonic (with passing note): EGA(Bb)BDE
To avoid wrong notes, remove from the instrument any keys that don't figure in the chosen scale. Also, extrapolate the scale over the range of the instrument using the high A key etc.
Oh, and what is a pentatonic scale? Any scale containing only five (different) notes. Many have no semitone intervals, making them easier to sing in than diatonic scales. You don't need a xylophone to try these out. Play them on whatever you have to hand.