Psychonauts (the original, not the sequel, though the sequel is also good) is a Summer Camp themed 3D platformer. It doesn’t quite meet your “low stakes/chill gameplay” criteria as it does have combat and mildly challenging boss fights and platforming, but it nails the rest. It’s easier than Tunic. Maybe worth checking out.
Brothers: A Tale of Two Sons strictly meets all the criteria listed, but it’s ultimately a tragic story. If “some kind of impact” includes leaving you in tears, check it out.
Okami is a Zelda style adventure set in feudal Japan with immaculate vibes. You play as the sun goddess Amaterasu in the form of a wolf bringing light and life to a land ravaged by demons. The world is cold and dark at first, but you bring spring and summer on your heels.
Finally, two favorites from my childhood are the Spyro series and the Ty the Tasmanian Tiger series. These are 3D Platformer collectathons and neither of these series are even close to any of the examples you provided, but they are bright and colorful and in my heart they have feelings of Summer Vacation and staying home all day to play video games.