Alex calls his father and his mother Pee and Em, for Pa and Ma. We only see them in three scenes, and they display varying levels of concern for their son. In the first scene, Em tries to wake Alex for school, but neither she nor Pee seem that worried that he never actually goes to school. Their parenting style can be best classified as "bad."
We see them again after Alex undergoes the Ludovico technique. They are scared of him because they realize what a horrible person their son was. In this scene, they seem like whimpering idiots. Pee is afraid of Alex and Em cries. Maybe they're regretting not putting their feet down with lil' Alex?
In the end, they decide to take Alex back in, and take responsibility for his actions. Pee says,
PEE: When you think about it, son...maybe it was our fault too in a way...
If that's true, though, what could they have done differently to change Alex and protect society from his psychosis?