There is no limit on what the teachers are teaching- just let the parents know!  Thats all we are asking for.  Shoot, it could be "mary had a little lamb" but all we are asking for is that parents be notified of the materials being taught or read as assignments.  

I presume you want parents to be more involved in the education process - and some will choose TO be involved and others will not.   But for those who want to be involved- dont make it harder. Just keep them informed.  Sensitive material or otherwise.   This appears to be a no-brainer.  And who knows- you may just educate a parent in the process.