In the US, the Children's Online Privacy Protection Act (COPPA) is the guiding legislation with regard to how to market to children. This includes email marketing, so it's important that email senders ensure compliance and aren't found to be doing anything that might result in marketing to children without a parent's consent.
COPPA is in the news today. The Minneapolis Star-Tribune reports that "a coalition of nearly 20 children's advocacy, health and public interest groups plans to file complaints with the Federal Trade Commission [today] asserting that some online marketing to children by [five] well-known companies violates [COPPA]."
I can't speak to the merits of the complaint, as I don't have all the facts. But it does highlight to me that if you're guiding marketing for a big brand or other well-known company, it's very important to make sure one stays away from anything that can be perceived to violate this law. By my reckoning, the FTC has levied fines against and/or come to costly settlements with at least eight different companies due to alleged COPPA violations.