SummaryCompaniesPM tells parents: 'We have your backs'Ban set to take effect in DecemberOther sites objected to YouTube's exemptionSYDNEY, July 30 (Reuters) - Australia said on Wednesday it will add YouTube to sites covered by its world-first ban on social media for teenagers, reversing an earlier decision to exempt the Alphabet-owned (GOOGL.O), opens new tab video-sharing site and potentially setting up a legal challenge.The decision came after the internet regulator urged the government last m...