The character of Pugsley was played by the child star Jimmy Workman, who retired from acting in the early 2000s. Despite a slight five-o'-clock shadow, he looks like he hasn't aged a day, even sporting the same signature spiky hair.
Christopher Lloyd did such a great job playing Uncle Fester that many didn't even realize it was the same guy who played Doc Brown from Back To The Future. He still has a busy schedule and looks better today than he did in his Uncle Fester makeup. Though to be fair, that's not a high bar to clear.
In the 1993 sequel, Addams Family Values, Grandmama was portrayed by Carol Kane. This was just another in a long list of comedic masterpieces she was featured in, including Annie Hall, Taxi, The Princess Bride, Scrooged, and the recent Unbreakable Kimmy Schmidt.
Mercedes McNab made a cameo in the original film as a Girl Scout, then returned for a much larger role as summer camp ice princess Amanda Buckman in Addams Family Values. We watched her grow up playing these parts, and also as Harmony Kendall in Buffy The Vampire Slayer.