Parents appreciate the easy access and variety of materials to help their pre-kindergartner practice basic skills.
1. Should 'pre-kindergartner' be pre-kindergartners? 2. Because we don't know how many children 'Parents' have, could be 1 or 2. Many times I see 'Parents', it'll will go with
I agree that pre-kindergartners should be plural, but maybe the thought is that even if parents have several children, they only have one pre-kindergartner who needs to practice basic skills..
I'm afraid I can't help with a rule -- I think people sometimes use singular and sometimes plural in situations like these without giving it much thought. Sorry! if you want to post more examples