Two boys lived in a kind of orphanage, I guess. There, the people responsible for them used “happy” or “sad” face stickers in order to control their behavior.
One of the boys had got too many of the sad stickers and the guy responsible for him said that because of his bad behavior he couldn’t go to a trip the other kids would make.
But the boy’s brother put him in his bag and so they both went on that trip (it was a kind of camp).
I don’t remember the ending, but I think the whole point of the willing of those boys to go there was to find their mother (she took them there once or something like that).
I don’t know if they were actually orphans.
I remember this scene where one old man was carrying the boy’s bag into the travelling bus and said “oh, it seems as if your own weight is inside it. What are you carrying?” and then, after the boy got to the seat and opened the zipper a little, his brother got out and said he almost couldn’t breathe and that in the way back home, the other one should go inside the bag.