This has a large thumping heart deep down, where clearly the Dardennes brothers (Luc and Jean Pierre) want these characters to make it through some how and some way in their dire circumstances. There is (as David Erhlich notes in his review) anger underneath all of this, anger at how embedded exploitation of the undocumented are, how no one (insert meme) will think of the children and so on, how everything comes down to "where are your papers" and an absence of emapathy.
That may be enough for the film to power through in depicting these kids, Tori (Schils) and Lokita (Mbundu), who are exceptional as child/teen performers go for what they're asked to show and embody. This does work as a tension-filled thriller especially in the second half, but compared to some of the other Dardennes films it is almost expectedly sad and, when seeing Lakita in her indentured servitude in the Marijuana farm it becomes even sort of dreary as a stark drama of circumstance and dread.
This isn't to say the film isn't worth seeing because it does keep you absorbed into both of these kid's plight and also how resourceful and quick on his feet Tori is (you think they will be apart for three months but hey not so fast, guys). But once the Dardennes get us to that ending, for all of the film's virtue and how much heart Mbundu puts into her performance in particular, it all feels like "well... that really sucks" and the catharsis isn't as powerful as it should feel.
Maybe that's more my problem than yours, but since everything has been presented at such a Naturalistic slice-of-life key, that moment just feels like it... happens, and it just reminds me why I'll always hold something like De Sica/Zavatiini's Shoeshine - also about kids lost in a prison they can't escape until it is too late - in such higher regard because it goes for real *and* melodrama and feels more ambitious.