I really loved the emotion created during the ride in the truck. The atmosphere of loneliness was very well done. The transition to night with the view of the moon overhead as the truck was moving along really worked for me. I really felt like I was there with him and it reminded me of my childhood (not being lost of course but riding in the car watching the sky and hearing the sounds of a summer night).
There are some elements that could use some work if you are interested.
The animation had a definite style and emotion but the sound effects of the scene where the boy sneaks into the truck didn't "match" the style as a whole. I don't think those sound effects were needed at all.
The "flashback" memories could have been more "stylized". I could tell that's what they were intended to be, but it wasn't as clear or as strong as it could have been. Some interesting effect, more desaturation, just some ideas.
There was one aspect of the story I wan't 100% sure of. Did the boy sneak away to FIND his mother? Or did he sneak away and then feel bad that he was lost and missed his old life? That part was not totally obvious to me. If he ran away and then ended up back where he started some elements of the original scene could have been used.