Upvote:4
Since you say "out of state", I'm going to guess that this is domestic travel within the United States.
At the major US airlines, a domestic round-trip ticket is generally the same total price as the two corresponding one-way tickets. (Years ago you could expect a round-trip ticket to be cheaper, but that's generally not true anymore.) So you can book a one-way ticket for yourself from A to B, and a separate one-way ticket with two passengers (you and your son) from B to A. The total fare will likely be the same as if you had bought a round-trip for yourself and a one-way for your son.
This has the added advantage that you can use different airlines for A->B and B->A, in case one airline has a lower fare on A->B and a different airline is lower on B->A.