Board Thread:General Discussion/@comment-6677347-20131227002040/@comment-124.184.83.137-20140113034243

Option 5 equals the child being only human, due to the fact that not all generation in the Grimm's family tree have Grimms

Option 6 equals the child being only Wesen (excluding hexenbeist), if the child doesn't turn Grimm, then it is essentially Human andhas a 50% chance of turning Wesen.

There isn't any real way of telling due to the concept not having been explored through the show as of yet.