Dear Jim,

Thanks for the question.  

You may have to gloss over the distinctions for now; when he is older as a young adult, you can talk more in-depth about your choices and differences with the Catholic faith.  

For now, I would simply say the least possible, unless questioned, whereas you can simply tell him that you go to a different church, and you do things differently there.  I would also affirm that both churches love Jesus and want to do everything He told us to do and that you are very proud of him for doing things to grow in his faith in Jesus.  

The most important thing that you can do for him is affirm him and let him know that you approve, love, and want to encourage him to know Jesus.  Ask your son to say his nighttime prayers and to pray for daddy, just as you do for him.  

Right now, this is more about relationships than doctrine, so keep it simple.

Peace,