Why are some parent's not getting emails from the system?

By default, system emails come from a no-reply email address which is standard with any sort of bulk or automated emails. This type of email address can sometimes be marked as spam depending on each individual user's spam settings. 

Spam settings are specific to each user's mail client and settings so there is no way to ensure that it will not be sent to spam folders for parents. What we can offer is changing the "from" email address to a valid email address like [e-mail], changing it to a valid address may help with emails going to spam but it does not ensure that every parent will get the email in their inbox rather than spam. 

You can update this by going to SETTINGS >> General Tab and updating the "Reply-To Email:" box.