It's a French movie. It starts out with a little girl being teased because she is (I think) Polish. A boy, who's Mother is dying of cancer befriends her. They have a pretty tin box that the boy's mother gave him and they trade it back and fourth daring each other to do naughty thing. They both get into a lot of trouble but as the kids become adults the film gets kind of dark. They are not romantic with each other but they do love each other. It's not a kids film (it's rather dark) but I really liked it. The title in English is something about children's games, I think. Thanks.
Is it called "Love Me if You Dare"
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Love Me If You Dare?