Is the family quite religious? I only ask because some people just do these things and would have no interest in the gifts I'm about to suggest wink If they are quite into their faith a nice set of rosary beads could go down well. Or perhaps a wall mounted prayer. A little bible or missal for church, a religious bookmark or guardian angel statue? The little shops out the back of a lot of churches have nice things as do St Vinnies.
Otherwise I would just give him a first communion card.
Here's some more ideas
http://www.labefana.com.au/boys_communion.html
This website has room blessings on pewter plaques specifically for children.
http://store.christiangiftsplace.com/pewter-room-blessing-plaques-by-cynthia-webb-p891.aspx