The Orc raiders are two of the most characterful sculpts from the GW Orcs and Goblins line. In my opinion, they are the most appropriate for an Orc warband in Mordheim. Thus, I would like to congratulate you and your son for finding them and using them. I have always believed that a family that plays together, stays together!
I also have a 5-year old boy who has exhibited signs of interest (much to the consternation of his mom who thinks that the hobby is too violent and mature for his age).
Keep up the great work my friend!