The displeasure Stan Lee often voiced regarding teenage sidekicks is well-known and even though DC has occasionally made adjustments that solve the dilemma, the Marvel legend actually found his own fix sooner. The mantles of heroes like Batman may have passed down to young heroes on occasion, but a Marvel spoof series drove a sidekick into his mentor's mantle easily. Not Brand Echh allowed Lee and other writers to try out new ideas and this one was certainly to be expected in some regards.
Not Brand Echh began publishing in 1967 and it ran until 1969. This Marvel series was brought back for one additional issue in 2017. It's a satirical comic that allowed writers to take humorous jabs at Marvel and other comic companies and characters. Stan Lee was known for not wanting teen sidekicks around, killing them off at every turn. He believed teens would be much better as heroes than merely sidekicks, as in the case of Spider-Man. He made another teen sidekick a hero in a much darker way within Marvel's spoof series.
Bucky Barnes was one of the most famous sidekicks that Stan Lee killed off. However, in Not Brand Echh #3, the story "The Honest-to-Irving, True-Blue, Top-Secret Original Origin of Charlie America!" allows a variant of Bucky to live. This story was created by Stan Lee, Roy Thomas, and Tom Sutton. Charlie America is a spoof of Captain America and is his opposite in every way. Charlie's a draft dodger and coward who tries to avoid conflict. He uses a trash can lid for a shield and his sidekick, Bunky, isn't exactly a fan of his mentor. Ultimately, Stan Lee allows Bunky to become the hero in a surprising twist.
Charlie America's story follows Captain America's closely and in it there are claims that Bunky was killed, just like Bucky. However, by the end it is revealed that Charlie America was the one who died and Bunky survived - thus being able to take up the mantle himself. In a twist of events, Stan Lee killed the mentor, freeing up the path to heroism in a different way. In Marvel Comics years later, Bucky has been known to take up Captain America's mantle - but this occurred much later than this spoofy origin.
While Batman's former Robin, Dick Grayson, has taken up the cowl himself, it took many years. The first time Dick wore the cowl was in the storyline "Batman: Prodigal," which began in Batman #512 in 1996. Following Bane breaking Batman's back, his mantle was taken up by Jean-Paul Valley, who ultimately failed at the role. This left the door open for Nightwing to step in temporarily while his former mentor recovered. Later, in 2009, the storyline "Batman: Battle for the Cowl" was a major crossover beginning in Gotham Gazette: Batman Dead? #1. It followed Final Crisis and within it, Dick Grayson once more took on the mantle of the Dark Knight.
It seems like a natural progression for the first Robin to wear the cowl, but it took a long time to actually happen. This is especially true since Stan Lee allowed his own variant sidekick to take on a brief, bigger role almost thirty years sooner than the publication of Dick's Batman role. It may have been only in jest, but Bunky definitely had it better than Bucky and Dick when it came to being removed from their sidekick roles - via death or substitution. Stan Lee may not have liked teen sidekicks, but unlike DC, he was prepared to take a humorous chance on throwing them into a bigger role.