Kimberly Henderson has always wanted to be a singer and after a video she posted on Facebook of her singing the Whitney Houston hit “How Will I know” as she rocked her toddler daughter went viral, it looked like her dream would come true. Even if the 26-year-old single mom of four kids was rejected by both “American Idol” and “The Voice,” her YouTube video got millions of views, and now record companies are courting Kimberly to sing for them. She’s already released her first single “Tiny Hearts,” which was inspired by unexpected motherhood.Kimberly became pregnant with her first daughter...