Simpkins made his film debut in Steven Spielberg's War of the Worlds (2005). Next was a featured role in All the King's Men (2006) where he played a young version of Jude Law's character, and he played Aaron in the multiple-award-winning Little Children (2006). Simpkins went on to film Pride and Glory (2008), in which he and his sister, actress Ryan Simpkins, play the children of Colin Farrell. Simpkins also completed Gardens of the Night (2008) and then Revolutionary Road (2008), in which he again starred alongside his real-life sister Ryan. Simpkins has guest-starred on CSI, Private Practice and Family of Four. In September 2009, he signed on to play Luke in the 2010 film The Next Three Days. He also played Dalton Lambert in Insidious (2011) and Insidious: Chapter 2 (2013).