Floor plan of semi-detached house 135m2, two full floors

I don't see any major blunders now, except..!
But in the kitchen, it is not a cooking island, that should be known.
Shower on the ground floor, does it have to be there? It's already very, very tight under the stairs. Utility room accessible from the living room, there are worse things. I would work with a hidden door there.
I don't like the bathroom upstairs at all: Dark washbasin, shower at the window: I would swap shower and toilet and replace the bathtub with an asymmetrical one measuring 90/160 cm.

Also: I would use the front door as a patio door and make the kitchen accessible right after the 70 cm wall stub. Then the kitchen as a U-shape, having the countertop at the bottom of the plan and going into the U. Wide tilt-turn window at countertop height facing the terrace, and the vacation can begin.
What is going on with the staircase in the upstairs bedroom?

Then consider your life rhythm with two children. Which part of the garden will they use and what paths will they take for that? Don't just think about your private cozy coffee spot, but about typical family life – with a large terrace in front of the kitchen, I boldly claim that the path for the whole family will permanently go through the kitchen. Therefore, I would place the living room there. But maybe your family life is oriented differently. Then it can make sense.

Thanks for the input. We thought about reversing it but found it more disturbing if everyone walks through the living room with shoes. That's why there is no door from the living room directly to the garden, but only the lift-and-slide door on the south side and the terrace door at the kitchen.

We thought about reversing it, but found it more annoying if everyone walks through the living room with shoes on.

Get used to the fact that the children and their friends don't really care what you think. Otherwise, it is common to have the terrace (at least the main access) in the living room. No criticism, just a note.

And otherwise it is common to have the terrace (at least the main access) in the living room.

Well .. but this is not a recommendation from me, for example, because I see it similarly to the OP that usually you need garden access from the kitchen. And the sofa/TV area is more the quiet chill-out corner in the house.

However, the kitchen must be planned more sensibly than with 2xL.
I would suggest moving the terrace door a bit further to the left according to the plan, so that about 70-75 cm of wall remain to the left of the terrace door. That should be enough, then on the left

275 cm tall cabinet block = yellow - wall stub 75 cm below in the plan
Terrace door - wall opening 125 cm below in the plan
240 cm cooking surface row (which I would prefer) or sink row = orange
240 cm peninsula = blue

And otherwise it is common to have the terrace (at least the main access) in the living room. No criticism, just a note.

What is common anyway? That was how it was done in the past, when the kitchen was still seen as the woman’s workroom and guests were received in the living room in front of the large panoramic window overlooking the well-kept show garden. Meanwhile, many have realized that the kitchen belongs to the terrace, where life takes place in the summer. The living room is more used for chilling and guests sit at the table. This is the lifestyle that the now young family generation has inherited from their predecessors. And it’s good! Whoever can afford to build like this does it right for the next 10/15 years. But we old ones built like that too.

What I also notice .. the staircase is quite steep with a rise of 19 cm and a tread of 24 cm, and the tread is quite narrow.

What is the "change" in the bedroom meant for a later staircase? Have you checked what heights you actually have there in the hip roof?