Kristin Cavallari and Chicago Bears quarterback Jay Cutler are expecting their first child, a source close to the engaged couple told Us Weekly. "She is really happy. She is in the early stages, but she can't wait to be a mom," the insider said of the reality TV star. "They have just bought a house in Tennessee and can't wait to start their family." The baby's due date and gender were not reported. Cavallari and Cutler have been dating off and on since August 2010. They announced their engagement in November. Cavallari is best known for her work on TV's "Dancing with the Stars" and "Laguna Beach."