Extension plans for a single-family house from 2 to 4 children's rooms. Ideas welcome!

if you are negotiating with parents below, I would do more remodeling. 1. set up the bedroom. The closet will be heavy. I would place the bathroom closer to the guest room. Because sometimes friends of 4 children stomp up and down, not necessarily in the middle of the day. Really think about where the freezer, 2. refrigerator, drinks, pasta, toilet paper should be stored. Just thinking about the amounts of fries, chicken wings, drinks consumed on Halloween is enough. Those are quantities that need to be produced off the cuff.

Apart from my usual nitpicking (I miss "Child 4" and I think the left-of-center ridge beam is incorrectly drawn), the question arises for me as to why there isn’t more lateral thinking (which of course does not mean the new "Querdenken" of the conspiracy theorists). Couldn't one, instead of dedicating the over-standard rooms to the over-standard children, switch things around and reshuffle the cards? That is, move the parents' area to the north gable – parents usually only use their sleeping room at night. What kind of triplets are these, actually: identical, and what is the gender mix of the entire brood (as well as the age gap of the older siblings)?

Good morning dear ones! Our goal is to offer all kids a nearly equally sized room. Where that is not possible, we upgrade the room (dormer). Since we only use our room for sleeping at night, we are willing to manage with just over 10 sqm. My wife is an engineer and a Tetris fan. she loves optimizing and compacting. And you should see us sometimes waking up with 6 people in bed :) It's not a luxury (meaning the 10 sqm is not, waking up with everyone in bed somehow is), but on the other hand, we don't want to live in a palace when the kids have flown the nest... Regarding storage space: point taken. We will definitely keep an eye on it. The wardrobe will have cupboards on both sides. Partly for clothes, partly for sweets for Halloween ;). If there is any space left, storage for popcorn maker, crepe maker, deep fryer, air fryer, crockpot, blender, Thermomix, wok... Just kidding, we don’t have a wok. The second fridge is already in the utility room. We don’t have a cellar, but a nicely finished attic (thanks to short-time work). There is even some space there. About the children: The girl is 5 years old, the 3 boys are now turning 3 (each).

:D
It seems that a bed enlargement is more necessary.
Perhaps you can plan the parents' wing and the living room extension so that a small granny flat can be created.

The kitchen already exists in its form as such?

Is the kitchen already existing in its current form?

The black part is existing. It will be added to an already inhabited house.

but on the other hand, we also don’t want to live in a palace once the kids have flown the nest...

You’re funny: what kind of WF numbers are those? I find the kids’ rooms quite large. Or are those just floor areas?

Just kidding, we don’t have a wok.

funny again ;)
The wok also stands for other stuff.
https://www.hausbau-forum.de/threads/die-liste-die-jeden-bauherren-zu-interessieren-hat.34418/

I think the idea of a granny flat (later) is not bad.