Custom Post Types and Child Themes!

In away, if you change basic functionally of the parent theme then you should not use a child theme. Child themes should be used to extend or override functionality but not change it. How can you tell the difference between extending and changing? You can’t :(.

In other words, the best place to ask is the author of the theme. It might be that he will never release an update or an update that he will release will introduce incompatibility with your child theme.