Welcome to my first story! I have been reading quite some fanfics last year. Since I have my own opinion, I decided to add all my thoughts and things I imagine that happened, in one story. I might 'steal' some elements from different stories I read as well (if I can find the original story and author, so I can give credit), since there are some things that inspired my version.
Here are my short notes for the children, since I know that can differ:
Liesl: mother's daughter, cared for the rest of the family after her mother passed away, stands up for her siblings.
Friedrich: tries to be like his father, second one to care for his siblings/family after his mother passed away, soft spot for Marta, teases/has arguments with his siblings, got the most in trouble (with Louisa), rivalry between Louisa and himself, trying to make his father proud.
Louisa: was close to her father, looks like her mother but her characteristics are like her father, teases/has arguments with her siblings, got the most in trouble (with Friedrich) which made her bond with her father worse, runs faster than Friedrich even though he is older, rivalry between Friedrich and herself.
Kurt: trying to cheer everyone up (especially Gretl), got in trouble often (not as much as Louisa and Friedrich), trying to make his father proud, loves food, rivalry between Brigitta and himself.
Brigitta: was close to her mother, loves to read, huge imagination, notices a lot, acts older than her age, rivalry between Kurt and herself.
Marta: shy but has a lot to say, the one who pleases, secretly her father's favourite, best friends with Gretl (and Friedrich, who has a soft spot for her). Loves pink, purple, dress up, dolls, tea parties, horses and ballet.
Gretl: best friends with Marta and looks up to her, loves to be around Kurt (and Marta/Liesl), sees Liesl as a mother figure, a bit more adventurous compared to Marta.
Don't be afraid to voice your own opinions, and let me know what you think would've happened, or what I should add!