Is it possible to filter a pages section in a blueprint by the content of its children?
In my example i have a news page with news-items as children. In the blueprint i want to display only the children with a certain category (the ‘category’ is a select field with some categories.)
No, that’s not possible.
If you only want to display these pages (without an option to add new items), check out the https://github.com/rasteiner/k3-pagesdisplay-section plugin
Cool this plugin helped a lot. i just added 2 page sections. one usual one fo create drafts and the other one with this plugin. small workaround, but in the end exactly what i wanted 
Thanks for the hint!