I agree with KS. Toomics doesn't have many kid-friendly comics, but Roblox is okay for 8+ because it doesn't have many violent games, scary, yeah a bit, but there aren't any se*ually suggestive or violent games and in the chatroom they tag out any swearing, mature content, passwords, links, phone numbers, etc.
Many kids are already using Roblox, so Roblox is safe with parental guidance.