Try alternating starters, Play your son for specific rotations, Try him in for run/pass play situations, depending on which he's better at. By "not" playing him, he'll lose confidence in himself, and maybe your Father/ Son relationship. On the other hand there, the examples above should be viable options of being fair as well as being the Father and wanting your Son to get his chance. Who knows, with some playing time, he might become an outstanding player. If he does not play, you will never get the chance to find out. Advise him, don't criticize him. Nothing a kid hates more than being lectured. Boost his confidence without overdoing it. Hopefully things will work out. Good Luck, let us know.
Oz