This wasn't my favorite Dardenne Bros. film but I like everything they do so I'm always excited when they put out something new. Some of the key plot points in this film are a bit implausible but I suppose that doesn't matter in the end.
As far as this being a modern 400 Blows, I definitely see that but it is not even close so making those sorts of comparisons does this film a disservice.
I like to think about this film as what might happen to that poor kid from L'Enfant about 10 years later. There are so many heartbreaking moments in this film that are made bearable by being offset by the heartwarming ones.
All told, this is a good but not great movie and not the place to start if you've never seen a film by the Dardennes.