"We welcome Scarlett May Stuber into our family. Our hearts are bigger with you here," Sims captioned a photo of the new baby girl.
The two, who tied the knot in 2011, are also parents to a 2-year-old son, Brooks. She announced last September that she and Stuber were expecting a second child.
"We are so, so, so blessed as a family, and I’m speechless at the fact that we have the opportunity to bring a second bundle of joy into the world," she wrote on her website. "As a new mom to Brooks, an entire world of motherhood opened to me along with a thousand and one questions. I absolutely cannot wait to see what life will be like as a mother to a toddler and a newborn."