Hit it with a hammer and get him an Italian type. The repertoire for six-hole English ocarinas is inane crap and their fingering system is tortuously bizarre. The Italian ones can play the entire bagpipe repertoire and then some (as they are more chromatic than a bagpipe with a range up to a major third wider), with fingering principles that transfer to or from other woodwinds.

I have a (rough) fingering chart for those on my website:

http://www.campin.me.uk/Music/Ocarina/

But as I point out there it makes no sense as a first instrument - it's far too difficult to play accurately in tune.