Single-family house ~190 sqm, three children's rooms, no basement - feedback would be great

The draft shows unclear priorities of the builders. On the one hand, you want to integrate special design aspects like a gallery, on the other hand – as you have also noticed – the children's rooms are quite small.
Look at your draft from above under the aspect "who or what gets how much space." I find the ratio of the garage wing to the house incongruous; the house has a far too small share of the ensemble.

The idea of placing the residential building "top left" has something special. You have space. My preference would be an L-shaped bungalow with a living and a sleeping wing. I would place the garage / workshop etc. near the street on the property as a separate and visually corresponding building. The access path would be close to the edge of the property and would separate a strip of kitchen garden for vegetables etc. from the rest of the garden. There would be a beech hedge towards the street.

By the way: I fully understand people who want to integrate design aspects into their house. Good design is never detached from function and serves the whole.

Still don't understand why the house is positioned like this. Please mark everything.
Dissolve the gallery on the upper floor.
There is no space for towels, toiletries, and a second sink in the bathroom would not be a luxury.
The children's rooms could also be a bit larger.
If the wall to the dressing room is removed, where will you place the wardrobes?

I would scrap the ground floor.
Remove the hallway to the building services, make the pantry bigger.
Possibly use the study as a children's room and have a smaller one upstairs with about 8 sqm.

I find the living, dining, kitchen area not successful at all.
Huge living room like a ballroom with kitchen and dining area cramped in.

[Alpenländisch Eckbank] sounds like a bigger living kitchen.
Cooking and eating facing each other.

Take a look at Heimat 4.0 by Baufritz. It also has 3 children's rooms.

Because otherwise the planned entrance would constitute an overbuilding of this tunnel?

Correct. However, that would be permissible.

The plan is a disaster. It's only good for the trash can.

Phew, everyone here seems to have a nuanced perspective. To understand the situation of the house, tunnels etc. should be drawn in. To bring the gallery in line with three children's rooms, one should consider extending the house by half a meter or so... anyone who puts up such a building for the cars could also do that.