"I've always wanted this," Henderson says, though she's shocked at how her career came about

Kimberly Henderson is one person for whom Internet stardom has translated into real-life success.

The South Carolina mother of four, 26, is experiencing a roller-coaster ride after a video of her singing Sam Smith’s arrangement of Whitney Houston’s “How Will I Know” to lull her baby to sleep went viral in December.

A single mother who had recently auditioned for American Idol and The Voice, Henderson found that her story resonated with people: her original video on Facebook has tens of of millions of views.

Since then, she’s been flown around the country, recorded a rapidly rising single, “Tiny Hearts,” and met with record labels and songwriters in New York City and L.A.

After the success of the video, Henderson tells PEOPLE, “an artist development company [Break Entertainment] reached out and they partnered with Cosco Kids and flew me out to L.A. at the beginning of January to record ‘Tiny Hearts’ That happened really fast. I was only down there for like four days. I wrote it with two other people and we had it recorded and made a video for it in like a day.”

Henderson has been singing and writing songs since she was 15, when she got pregnant with her first child, which inspired “Tiny Hearts.” “I got pregnant when I was 16 because I didn’t have a lot of direction,” she told Cosmopolitan. “I’m not blaming that on anyone because that was my choice at the time, but I didn’t know anything about periods or boys.”

She’s come a long way since then: Henderson has a manager – Susan Markheim, with Irving Azoff’s agency – and is in talks with major labels and publishing companies.

“It’s almost unbelievable,” she says. “I’ve always been a singer, I’ve always sung to my daughter, and I’ve always wanted this, but for it to come from just a simple video I made on my phone of me singing to my kid it’s absolutely nuts.”

And Henderson’s kids share her excitement: “My girls are like, ‘Mom, everyone at school thinks you’re famous, and everyone likes us!’ They had a sleepover last week and all the kids came and were sitting around saying, ‘You’re so famous.’ It’s so funny.”

And her costar in the video? “Well, Vaida doesn’t really know what’s going on. As long as she gets fed and gets her diaper changed, she’s good to go.”