Floor plan for a single-family house with 4-5 children's rooms

Probably true. My spatial imagination is too poor.

Then our bedroom in the attic. Is that also the case now and the playroom downstairs?

The Hanse Haus will exceed your budget.
Take the development plan and sketch out how much attic space you actually have.
Then write down which rooms you currently need and their space requirements. Your measuring tape will help you.
Then imagine your life with the gang in 7-10 years.
Consider which rooms can have multiple uses.
For example, now a family bedroom, later quiet and a bedroom for two. What do you want to do with the oversized bedroom now?
All-purpose room - great, you have everything in view. Later you want to have coffee quietly with your girlfriend. There is no door.
Playroom sounds great. Honestly, from when and how long will the children play alone in the attic?

You have a limited budget and cannot plan every room large enough to cover all eventualities.

Would have also gone the route of the planned conversion. Today, the sleeping floor is completely upstairs and downstairs there is a playroom as well as a common room; in kindergarten and teenage years a children's floor with a large play and entertainment corridor with its own couch corner, climbing wall, and whatever else you can imagine, with somewhat smaller single rooms, and the parents' room with an office corner moves into the former playroom on the ground floor. Regarding the bathroom, I would basically consider a hybrid... smaller bathroom and separate toilet. This way you would have more sinks and possibilities to get ready at the same time. The same on the ground floor, where the toilet could also be used as a guest toilet (access for guests would of course have to be considered here). The little ones will still play downstairs for a while but the older they get, the more it moves upstairs. I believe anyone who has such a "rasselbande" at home consciously wants to maintain some contact with their children.

Rough overview or proposal:
EG
- Allraum 45-50sqm
- Spielzimmer/Schlafzimmer 15-20sqm
- Bad/WC 8-10sqm
- Technik/Hauswirtschaftsraum/Mudroom 15sqm
- Flur 10sqm
--------
95-105sqm

OG
- 5 Kinderzimmer/Schlafzimmer 55-60sqm
- Spielflur 25sqm
- 2 Bäder +1WC (4+4+2) 10sqm
- Wäscheraum für Waschmaschine/Trockner 5sqm
--------
95-100sqm

I would say this can work with the budget but spares you some decisions on luxury problems :).

Many thanks for the concrete proposal! These are many ideas that I really like! And yes, we have deliberately chosen to live with four children and want to build exactly in their best interest. Play hall, mudroom etc. perfect! Washing machine and dryer upstairs is a great suggestion that somehow I have never come across before. It saves the pointless carrying down to the ground floor and back up again. And the separate bathrooms/toilets also make a lot of sense! I have to admit I didn’t know the term AllRaum. Is that what you call an open plan kitchen, living room, dining room?

I always find it interesting when everyone here says it has to be this big and that many square meters for children's rooms is out of the question. I wish our architect were more creative too… I can recommend a house on Instagram where a family with 3 children and little square meters has found very interesting solutions. Just as inspiration, to show that it can be done differently. I'll send it to you via PM since I don't want to unintentionally put the account in the public spotlight here, okay? Oh darn, I can't do that. Take a look on Instagram under Frau Gold and Sommerricke. There is somewhere a post about children's rooms with attic space.

Exactly, open-plan living in our case means kitchen, living room, and dining room combined in one large space. I have no idea whether the term is commonly used in everyday language or mainly established in forums; I wouldn’t bet on it appearing in the Duden :D

One thing seems certain from the start: you will have a lot of doors in the house... hence the approach to keep the purely transit area of the hallway as small as possible by simultaneously using it as a play area. Regarding storage space, I would try to plan built-in cupboards in some places in advance for commonly shared items like towels, toilet paper, games, craft supplies, etc., and then usual Christmas decorations, winter clothes, etc. up top... If it’s going to be a one-and-a-half-story house, there is also the question of whether you could design the hallway upstairs to be higher to create additional storage space above the normal cupboard height instead of having to haul everything up to the attic through a tiny hatch. In our case, the roof space is open, so we will probably have a built-in cupboard about 3.2 m high instead of the usual 2 m. -> but that would be something to clarify later as an option. If you’re considering a garage or carport (budget), it might be worthwhile to consider a pitched roof instead of a flat roof to store less sensitive items there. Additionally, possibly a side entrance door to the mudroom, so when the play clothes are all muddy they can be disposed of immediately in the “dirty area.”

@ moo Regarding the square meters and concrete numbers, my intent was to have a starting point, also in terms of a limited budget. There is always room to move in both directions. I think over time you should develop a sense of what you personally need, what you value, or what you can neglect. At the beginning, however, I found it very difficult to imagine something from the numbers, I measured a lot in various houses and gradually was able to develop something of my own. So first a standard suggestion and some ideas beyond the standard to engage with on your own.

So I am surprised that everyone here considers this feasible without reservation. I calculate: 220sqm x €2500 = €550,000 Additional construction costs €40,000-50,000 Kitchen and furniture €15,000 And I'm already completely at the €610,000 limit without any outdoor facilities. And without a terrace, you don't want to live at the house entrance forever. Besides, you have to manage €2500/sqm nowadays, and for example, a second bathroom also costs €10,000.