The number of social sites aimed at children under 13 is suddenly growing again. Now joining Everloop (which just raised another $3.1 million, TechCrunch reported), YourSphere (for young people under and over 13), and Togetherville.com (recently acquired by Disney) is WhatsWhat.me. National Geographic-branded AnimalJam.com for kids 5-11 passed the 1 million player mark in a matter of months with … [Read more...] about U13s on social sites: Who’ll get the equation right?