Music Key's to suit voice?

Help, no idea about music, but my son is trying to sing Cats in the Cradle. Plays it well on the guitar and puts his capo on Fret 3. He sings it well, but as a youngster he troubles with the lower notes and ends up being quiet. When he tries to sing in (what he tells me is a key of C) he ends up singing too high. He is asking me for a backing track the midi's I have found for him (6 in total), he tells me that they are in key of C. Does anyone know where I should be looking to get him a backing track at another key?? Thank you.