Now I have checked some more parts of this 1983 series (rating 9) including the last part which has uploaded to Youtube much later.
There is another older teen actress as main character Annemarie (Anja Bayer, pictured bottom left in a blue sailor dress in ep 6) and at least 3 younger boys in different white sailor suits, different age (pic bottom right, ep 6), outside scene.
I also checked again some earlier episodes. The big picture on top from ep. 2 showing the youngest brother in longer buckskin Lederhosen (on left with his older brother). The older brother told him, that mother forbids wearing the Lederhosen just for the streets, but he didn’t care.
The other 2 pics showing both brothers in blue sailor suits in ep 1. I prefer white sailor suits but the blue ones look also great on them.
For more infos see the main entry
I still haven’t seen the complete series, maybe I will even buy it. There might be even more interesting scenes and actors (eg at school). However main character is the 6 yo girl.