Looking for ideas to design a bathroom

The wall is 1 m high. There are flush tanks with a height of 1 m in front of the wall with top operation. Then ceiling-high glass.

We implemented something similar. The flush tank and shower drain are integrated into the partition wall, the window glass only goes up to 2.20 m high, as the entire T is not ceiling-high either. This makes ventilation easier.

I would like to move the door. It has two advantages: sightline when entering and space for the cabinet/shelf

Of course, it works like this too.

Shower and toilet swapped.

We implemented it similarly. The flush tank and shower drain are integrated into the partition wall, the window glass only goes up to 2.20 meters high, just like the entire partition which is not floor-to-ceiling. This makes ventilation easier.

I have the glass for the shower only 1.8m high. That also works. Maybe visualize whether it looks better not floor-to-ceiling. To better control ventilation, I would prefer floor-to-ceiling. Ventilation through WC and shower.

which one should rather avoid.

You avoid that when you want to accommodate 4-5 people in one bathroom and want to have some privacy when things go wrong.
Since you are planning a children's bathroom, that problem shouldn't even exist, right? A toilet these days is no longer an ugly outhouse.

Also, I'm not sure if 3.40m would be enough for WC + shower + sink.

Of course it is enough.

With the T layout, you look from the toilet at a wall... also not exactly nice.

At the T, you look from the toilet onto a wall... not exactly nice either.

If that bothers you, you can just make the window wider and/or move it. Or two narrow ones.