As it doesn't seem like anyone has strong feelings on this, I tried to put in a BUR as follows:
imply father_and_son -> parent_and_child
imply father_and_daughter -> parent_and_child
imply father_and_child -> parent_and_child
imply mother_and_son -> parent_and_child
imply mother_and_daughter -> parent_and_child
imply mother_and_child -> parent_and_child
...and got this error message:
Can't create implication father_and_son -> parent_and_child ('father_and_son' can't make up more than 90% of 'parent_and_child'); Can't create implication father_and_daughter -> parent_and_child ('father_and_daughter' can't make up more than 90% of 'parent_and_child'); Can't create implication mother_and_son -> parent_and_child ('mother_and_son' can't make up more than 90% of 'parent_and_child'); Can't create implication mother_and_daughter -> parent_and_child ('mother_and_daughter' can't make up more than 90% of 'parent_and_child')
What does this mean? Each of these tags would make up about 16%, 24%, .1%, 42%, 41%, and 1% of a combined parent and child tag. I'm not seeing over 90% anywhere.