Peter watched as Susan struggled with the boys at school, the clumsiness of first love and crushes in the air that she walked in. To be sure, Lucy noticed it in him, too, but he didn't.
Peter watched as Edmund struggled with his schoolwork, watched as he fidgeted during the designated homework hour, watched as his friends changed. Lucy saw it too, but Edmund never knew that she did, but Edmund knew that Peter watched. Lucy watched as the seeds of Edmund's betrayal to the White Witch were planted as her brothers shouted at each other.
Peter watched Lucy as she grew silently, sketches, poems, and paintings collecting on her side of the girls' room. Susan saw it too, and reveled in it.
Peter watched as Susan became bossy, as all girls that age did. Peter watched her struggle with puberty, as he struggled with it himself.
Peter watched helplessly as Edmund grew away from him, starting with a fight over Peter watching Edmund as he struggled with his homework. Lucy watched her sibling's faces as Susan jumped into the fray, trying to be peacemaker. Lucy saw how her siblings each started to go their own way as she sketched her siblings happy.
Peter watched Lucy become quieter, knowing that she, like Edmund, was teased at school. Peter watched his little sister grow up, but without acting on it, too immersed in his own problems.
Lucy watched, and put her thoughts in many poems and sketches that gave her side of the room a rather sad air.
Susan saw the wistfulness in Lucy's work, saw how her siblings had changed, but again, didn't act on it, of course being too immersed in the never-ending struggle to become popular.
Edmund saw his siblings with resentment, now, for pitying him, when all they had done was love him.