Floor plan single-family house, 3 children's rooms, goal: save sqm

If an architect was at work here (and not a draftsman for the contractor), then he must still be quite inexperienced. With a systematic approach (including the determination of fundamentals, which is a service provided by the architect at the very beginning of the design process and regularly does not occur with the draftsman), this typically only happens to novices, to exceed the building volume budget to such an extent. To this extent, it cannot be remedied through corrections; a new design is necessary.

I just looked at the plan upper wall: is that a canopy? Then the garage should be moved forward by one meter, door then to the side, then the view here would also be correct, if the external office window is also set back, because that doesn't fit at all. Yes, somehow 11ant is right with his assumption that no ambitious architect was at work here, everything is still "in the beginning" of the planning. Since there are already sections and views, please upload them here.

The purpose of the second corridor on the upper floor is not clear to me at all. Since there is only one bathroom at the end of this corridor on the upper floor, you cannot really speak of a separation between the parents' and children's areas. Leave out the open space, entrance to the bathroom from the "main corridor". Then access the utility room through the bathroom and designate the storage room (Abstellraum) as a dressing room and through this into the bedroom. This way, the house can be at least 1 meter narrower on the upper floor, meaning about 10m2 less area. Where savings can be made on the ground floor, or possibly move the living room under the balcony forward (bay window), would have to be seen.

Thank you for your feedback. I am grateful for every single one here. I am an absolute beginner in this field and had imagined it to be much easier. You think that when you build new, it is much easier and you can do everything however you want. Due to my little experience, I signed up here and have already received some good ideas. I really like 's idea of taking away the airspace, then the bathroom is accessible and I can leave out the entire second hallway (which bothers me anyway). That already saves me quite a bit. The airlock is our wardrobe. A built-in closet wall will go in here for all shoes, bags, jackets, helmets, etc., basically everything you have with kids... And I would like to go through the garage into the house a lot with the kids because of sand and mud, etc. We would then make a small guest wardrobe under the stairs. Regarding child 3, sorry, that is very confusing. We would initially use the office upstairs, and when child 3 comes along someday, then the office downstairs and child upstairs. We just didn't want to have child 3 everywhere in the plans. I have also considered starting over again. However, I really like the kitchen, dining, and living area. The kitchen is centered but not the first thing you run into. The living room is separable. Currently, everything is open with us. And personally, it just bothers us if the dishwasher is being emptied or cooking is going on or the Thermomix is running in the evening and someone else wants to watch something. Or some people want to talk at the table and others already want to watch something. Yes, I hope I was able to answer everything so far.

Also consider whether you should reverse the staircase, as this would give you more space in the entrance area, which is certainly not a disadvantage with 5 people. In addition, the wardrobe under the stairs is more easily accessible for guests. I would also add a window in the garage in the workshop area. Otherwise, in my view, everything has already been said. Nice floor plan!

@allesandro Good idea with the rotation of the staircase. That really creates more space. Thanks I am already thinking one step further; with the removal of the airspace, the above will become much more accessible and with a bit of shuffling we will hopefully be able to make it smaller. So that it is affordable and we still have some leeway for a few unforeseen things.