Floor plan planning shortly before submitting the building application

In A children's room I would also use A railing height, unless something like in a kitchen argues for a different railing height.

In ONE children's room I would also use ONE sill height, unless something like in a kitchen argues for a different sill height.

The changes now entail various things. If you uniformly lowered the sill height to 87 cm or similar in the children's room, you would have to do the same in the bathroom to avoid affecting the exterior appearance. And whether the toilet remains next to this window, as shown, or not; I cannot imagine such a low sill height in the bathroom - despite frosting... you would also have to consider the children's bathroom. However, it would definitely be inconsistent there, because at the front you would have to accept the downside of the low sill height.

At our home, everything is currently at an 87 cm sill height, except the bathrooms, which are at 110.

Because of these considerations, I thought the smallest compromise would be to work with different sill heights in the children's bathroom and for child 1 respectively.

I would say the top edge of the windowsill at 90cm. Then enlarge the windows accordingly so that the top edge remains the same, right?

Yes, of course. The lintels do not move down.

The bathroom next to Child 1 is only affected by the toilet position. To the north, you even accept a floor-to-ceiling window there. And instead of frosted windows, which I always find terrible, you could simply put a pleated blind there if you feel more comfortable on the pot at a height of 110 cm next to you.

Equipping a house for - ultimately around 1 million - predominantly with only 88.5 cm (!) narrow doors in the shell(!) construction phase at only 213 cm "raw" height is not exactly generous.
With the frame, that leaves only about 76 cm width and 201 cm height "in reality."
I don't have the room height in mind right now. Hopefully, it is high, so final 2.75 m +. Doors also need to grow with that.

Especially for the bathroom, bedroom, utility room, and above all the kitchen, in this class, otherwise, for me, a clear showstopper!

Equipping a house for – ultimately around 1 million – predominantly with doors only 88.5 cm (!) wide in the shell(!) construction phase with just 213 cm "raw" height is not exactly generous.

I showed the doors to the architect at our place and said they couldn’t be any smaller. I just measured the clear passage width again. It is 81 cm. I don’t want it any narrower. So if 88.5 cm is specified in the plan, do you think it will end up narrower? Then I will have that corrected.