The ending of film lost me a bit. After his disastrous press conference, Christian is seen at his daughter's cheerleading competition, then goes to try and find the boy, knocks on one (apparently) random apartment and doesn't find the boy, then is in the car with his girls looking like dead eyed zombies. I guess the film had to end somewhere, but it almost seems like they didn't know how to end it (or I missed the point, which is entirely possible).
That was an interesting last moment. I wasn't sure what to make of it either, but I think it could be a moment the girls are starting to see their father differently. Prior to that, he was shouting at them, at the boy, and who knows how many other times he's lost his temper irresponsibly in front of those girls. One scene shows them fighting like cats & dogs and screaming at the top of their lungs. They must've learned it from somewhere.
However, in the last scene, Christian attempts to right a few wrongs and actually tries to find the boy he callously neglected before, and he even goes through great efforts to do it. Perhaps the girls are impressed by their father taking responsibility (actually doing it instead of pontificating about it).
It would kind of tie into the movie's themes, about how people say
they are charitable and feel charitable, but don't really follow through with actions. As a reviewer put it, The Square both skewers elitist social bubbles, and highlights the ultimate "Hypocrisy of Man." Christian is all about making art that speaks universally about the need for deeper connection with their fellow man and helping the unfortunate, and yet, there are countless examples of him and others in his social circle not behaving anywhere close to the ideals they profess.