As someone whose favorite game as a kid was Kirby’s Adventure, yes, Kirby is supposed to be accessible to young children. 100% completion can be a bit hard. I remember Sakurai saying that he tuned Kirby to be the easiest to control in Smash games because kids like to play him. As an adult, they’re relaxing to play. They’re not all easy though – Canvas Curse might not be retro, but I think it’s hard!