It was announced last month that Hart would be stepping in to replace late comedy legend Jerry Lewis as the host of the annual fundraiser and now the comedian's "The Upside" co-star Cranston, Union, and "Tenet" 's Washington have joined a long list of celebrities who will make an appearance during the online event.
Garcelle Beauvais, Aloe Blacc, Adam Devine, Fat Joe, DJ Khaled, Daniel Levy, and Robin Thicke have also been added to "The MDA Kevin Hart Kids Telethon" line-up. They joined previously announced guests Jack Black, Usain Bolt, Josh Gad, and Michael B. Jordan.
Lewis fronted the big variety and fundraising show from Las Vegas over America's Labor Day weekend for more than four decades, helping to raise more than $2 billion for the cause. He hosted his last MDA telethon in 2010 and the event was subsequently scrapped as officials at the charity insisted the format was no longer relevant.
It has since been scaled down to a two-hour show, set to take place on 24 October (20).
"This is an incredible opportunity to bring the work of Jerry Lewis and the Muscular Dystrophy Association forward," Hart said. "I'm honored to collaborate with MDA and my organization, to educate and entertain the public about the need to support people with disabilities and disadvantages, because we are all in this together. I can't wait to have an incredible night for two critically important causes that are in urgent need of funding and hope."