By Daniel Kline,Danni Button The fast-food giant wants adults to remember their childhood with help from some old friends who haven’t been around for a while. (Welcome back, Grimace) McDonald’s (MCD) – Get McDonald’s Corporation Report used to build a lot of its advertising on the McDonaldland characters. This was a fictional world where Ronald McDonald, the chain’s iconic clown, lived with friends including Mayor McCheese, Grimace, and of course, notorious hamburger thief, Hamburglar. In later years, the chain added Early Bird (to promote breakfast), the Fry Guys, and a bunch of unnamed Chick…