How can a good Christian parent accept his child playing RPGs?
If you think of yourself as a good Christian, simply require that your child play RPGs in the way that they should do everything else – with good Christian values and as a testament to Christ. Maybe his character could be a knight sworn to Holy orders, or a peasant girl with a strong personal faith like the Christian girl in The Hiding Place. There’s no reason your child can’t play in a Christian way, and you can definitely make sure that the referee understands your standards for what is appropriate.