Reynir is the youngest child. He's a cheerful, ebullient, excitable personality, who feels like he constantly has to be useful. Which means that growing up (if his family is typical according to the families I'm used to) this happened a lot:
"Reynir, you're not helping."
"Go and bug somebody else."
"Ugh, you're so annoying."
"Reynir. Stop."
"Calm down already!"
Baby Reynir would be subdued for a few moments, then probably try to 'help' some more, leading to more explicit rebuffs. He would probably feel like a burden when he was permitted to help with 'grown-up' tasks, being significantly less able than his older siblings---probably his only peers. And he would definitely have the youngest child complex of needing almost constant attention.
Okay, back to why I'm upset: panel five, page 308.
".....Oooh. I got it. I'm sorry."
HE KNOWS THAT TUURI'S LYING TO HIM. HE KNOWS SHE LOCKED HIM OUT. HE KNOWS THAT HE WAS ANNOYING HER. This is just further validation of the "Reynir's annoying" he would have heard from his (still loving) older siblings. REYNIR IS APOLOGIZING FOR HIMSELF.
And then Mikkel shows up. "And I'm sorry to see you wandering around without supervision." *reinforces dependence* "You'll stay where I don't have to keep an eye on you." *reinforces that Reynir's a burden* Look at Reynir's face. He's chewing on his cheek again---which is what he does when he's confused/unsure/conflicted, etc. The next panel? He's trying to make himself less of a burden. "I didn't have nightmares." He's touching his neck---that's a clear body-language indicator of discomfort. Also an indicator of lying.
So there we have it. In just one page, Reynir is psychologically squashed back into place, is made, once again, to feel that he is nothing but a burden, a hindrance, and an annoyance to others. Probably the same way he was made to feel when he was a young child. Am I reading too much into this? PROBABLY. *retires sobbing into the night*