This question already has an answer here:
A letter home from daycare may be sensitive to the fact that some children have a single parent like this:
And if that same letter home wanted to be sensitive to the fact that I may have more than one child enrolled:
This letter is concerning your child(ren)...
But what if I have twin infants? (twinfants)
This letter is about your baby(ies)...
I believe the parentheses indicate that the letters within are optional, but do they also indicate that you should remove the y?
EDIT: The suggested duplicate has many suggestions, none of which is backed by a guideline or rule. Is there no rule governing this behavior?