This is an interesting entry, as Mason Vale Cotton isn't a former child actor, he still is a child actor - he's currently only 16 years old, but he has a lot of acting credits under his belt for someone so young. Cotton landed his first big role as a four-year-old when he was cast as Maynard James "M.J." Delfino in the television series, Desperate Housewives. He stayed in the role for five years, from 2008 to 2012.
Things have only progressed from there and we really see this kid going places! His next big role was from 2012 to 2015 when he portrayed Bobby Draper in the television series, Mad Men. A hugely popular show, Cotton is sure to just move up from here. He's also not shy about taking on voice work. In Hey Arnold!: The Jungle Movie, released in 2017, Cotton voiced the main character, Arnold.