Morte a Venezia (Death in Venice) is foreign-made at least, despite the absence of dialogue for nearly all the film, and has the famous ending - not really a beach, but certainly sand and water.
Ivanovo Detstvo (Ivan's Childhood) ends with a flashback sequence set on a beach, I think. This shows an inextricable link between childhood and the seaside - playing in open spaces, freedom etc.
Perhaps the significance of the ending of Les 400 Coups is that Antoine has reached a turning point in his life. Everything is stretching out before him (the horizon) - where does he go from here?
It's a really interesting subject, but I'm not sure of a common link between the endings.