Height of tiled walls in bathroom 1.2m or 1.5m?

So that plastered walls and as few tiles as possible in the bathroom look better is very, very subjective. I don't like that at all! I would look at many pictures on the internet and decide according to YOUR taste.

Many tiles above the windowsill height so that they have a wiping edge. You can certainly consider that, otherwise, if you are not careful, you will have a dirty window reveal.

So you don't need tiles at least in the parents' bathroom for the sink. The bathtub is freestanding, so no tiles there either. But of course, it's a matter of taste.

In addition to the mentioned bathroom furniture, definitely consider the mirror (-cabinet) as well. Where is the lower edge located?

So you don't need tiles at least around the sink in the parents' bathroom.

So yes, the kids do make a lot more mess. But even we sometimes get splashes while brushing our teeth, or when you clean the back area of the sink you reach the wall/tiles.

So I would always plan for tiles there.

we don’t have tiles all around in any bathroom, only where it is needed, so at the sink, bathtub, toilet and in the shower and as high as necessary there.

Did you also look for alternatives "back then"? I ask because I would prefer not to have tiles on the walls in any of the rooms. But without a convincing concept, I won’t get that passed with my husband. Aren’t there "such" glass panels nowadays?

because I prefer not to have tiles on the walls in any of the rooms

In most rooms, water is something you use to wipe away dirt - in the kitchen and bathroom, however, water is something with which you also splash some dirt around. What do you have against tiles?