I think you missed the parents point, no human has to read your mail to do those things. Google already has an image search which can filter out mature content, if they compare the md5 of your attachment to the images they've already flagged as mature they could identify you as a porn. The point is that "Transmit content that may be harmful to minors" is a very low standard and it's not clear how actively google will enforce the prohibited actions
Here's the complete list:
In addition to (and/or as some examples of) the violations described in Section 3 of the Terms of Use, users may not:
Generate or facilitate unsolicited commercial email ("spam"). Such activity includes, but is not limited to
sending email in violation of the CAN-SPAM Act or any other applicable anti-spam law
imitating or impersonating another person or his, her or its email address, or creating false accounts for the purpose of sending spam
data mining any web property(including Google) to find email addresses
sending unauthorized mail via open, third-party servers
sending emails to users who have requested to be removed from a mailing list
selling, exchanging or distributing to a third party the email addresses of any person without such person's knowing and continued consent to such disclosure
sending unsolicited emails to significant numbers of email addresses belonging to individuals and/or entities with whom you have no preexisting relationship
Send, upload, distribute or disseminate or offer to do the same with respect to any unlawful, defamatory, harassing, abusive, fraudulent, infringing, obscene, or otherwise objectionable content
Intentionally distribute viruses, worms, defects, Trojan horses, corrupted files, hoaxes, or any other items of a destructive or deceptive nature
Conduct or forward pyramid schemes and the like
Transmit content that may be harmful to minors
Impersonate another person (via the use of an email address or otherwise) or otherwise misrepresent yourself or the source of any email
Illegally transmit another's intellectual property or other proprietary information without such owner's or licensor's permission
Use Gmail to violate the legal rights (such as rights of privacy and publicity) of others
Promote or encourage illegal activity
Interfere with other Gmail users' enjoyment of the Service
Create multiple user accounts or create user accounts by automated means or under false or fraudulent pretenses
Modify, adapt, translate, or reverse engineer any portion of the Gmail Service
Remove any copyright, trademark or other proprietary rights notices contained in or on the Gmail Service
Reformat or frame any portion of the web pages that are part of the Gmail Service
Use the Gmail Service in connection with illegal peer-to-peer file sharing
Here's the complete list:
In addition to (and/or as some examples of) the violations described in Section 3 of the Terms of Use, users may not: