Where is a possible second bathroom feasible in the floor plan?

And is there still a staircase leading from the upper floor to the attic? And for how many kids are the children's rooms supposed to be? Or how are the upper floor rooms divided? If it is only one child (that's what I thought), then I would prefer the bathroom door. That way you gain some space upstairs. Why you now enthusiastically want to create a third bathroom is beyond me.

There is no attic… the house has a flat roof. And currently there is only a guest WC and one bathroom. That’s why the question about an additional bathroom. I don’t find the room layout on the upper floor ideal. 2 very large rooms and one small room… there are 2 girls.