Ground floor approx. 100 sqm, upper floor expandable (planned bathroom, 2 children's rooms, 1 storage room)

No, just don’t crumple it.
Whether the visitor looks for door a or b is their business.
But I came yesterday from the countryside, planted something, am dirty, back door, shoes off, pants off, immediately put in front of the Bosch, washed paws in the sink, dried on the dirty pants... indispensable comfort. A kitchen where you can sit, eat, chat, indispensable, a kitchen table for drinking coffee, peeling crab, with a wax tablecloth, that’s Schleswig Holstein. Sacrifice all that just because some describe it as last century? Then you’re last century, so what. Karsten

There is a lack of space. There is nothing against an open-plan kitchen, which is then properly sized, and a second dining table from the living room. A second door takes up space and standing area. You can also take off dirty shoes at one entrance and wash your hands two steps away. The OP is building a three-room apartment including stairs and building services. The floor area of an 80 sqm apartment is no longer available.

Can the "z" please be written in lowercase, just out of respect for the victims of the Shoah?

Thank you that was also on the tip of my tongue. Alternatively, just children's room...

That was not the reason to show it. It is an example of a usable yet not so space-consuming staircase.

That was clear to me. Your staircase is a model of symbiosis between space economy and walkability. Nevertheless, I find it worthwhile to reflect on the floor plan as a whole, whether it also fits here.

Back door, shoes off, pants off, put straight into the Bosch, paws washed in the utility sink, dried on the dirty pants... indispensable comfort.

Most of the time when I come home, I don't come from wallowing in the garden. Maybe that's why I go through the front door so often.

If you have little or no space, and money is not exactly plentiful, you have to make do with what you have. You can't have everything twice and show off space.

I come home _every_ day from work and/or somewhere else. I enjoy my well-kept entrance area that welcomes everyone, including myself. If I have been soaking a few days a year or have been working hard in the garden, then I go through the terrace door at the back or through the front door where the key is in the lock from the outside. Shoes and pants are taken off outside. You can also make many things more complicated than they are. Tip: don't focus on the few times a year, but on everyday life. If you build a closed kitchen because the kitchen party once a year is so cozy: forget it. Guest room for 2 guests? Nope, hotel is cheaper.

Focus on why you are building, what fundamental advantages a home has for the family, and make the best of the existing budget. No strange ideas about habits, everyday life will automatically adapt in the new house. But let the basics be right. I don’t see a daily routine here that would be easy to understand (getting up along the wall, not reaching the closet, not the bedroom window anyway, bathroom in front of the front door, then into the kitchen, gladly back for the Nutella bread in the living room, check everything, including the TV, then coffee again, long hallway makes you fit..., and then always that appendix in the eye [emoji848])

Please don’t consider me resistant to advice now, but I fear we won’t quite agree on this.

Reducing it to one door is out of the question for us. That really seems to be a regional peculiarity (I wasn’t aware of that until now), but we do not want to miss a door in the utility room.

However, we will take nordlys’ suggestion to heart: the children's room will only be accessible through the living room, and we will extend the living room wall to the bedroom. This eliminates the annoying kink in the hallway and removes the kink in the bedroom. Additionally, we should rotate the bed by 90 degrees so that it’s easier to access the window.