Ideas for the bathroom

I am looking for a few ideas for the bathroom.
Attached is a drawn floor plan. It is an existing building.

The wall to the children's room can still be moved. The room might currently be too large?
The wall next to the toilet is just an idea. As is the shower.
There is a sloping roof and it should be a double roof window.

I am not really happy with my ideas so far though. Maybe one of you has a great concept.

I would also like a large oval bathtub in a built-up base directly under the windows.

I would rather make the children's room bigger.

And this staircase is already there and works? Somehow steps are missing.

Currently, the bathroom has a width of 4m instead of 4.80 as on the plan. But either way, I find the planning difficult. The staircase exists and works. The number of steps was just not transferred correctly.

The toilet is not according to DIN if it is under 2 meters. A bathroom with 15 sqm is actually quite large, almost too large. I would move the door so that the room behind it is also furnishable.

Then maybe the rooms should be left as they are after all. The right wall to the children's room is currently, as mentioned, 80cm further to the left.

Swap the bathtub and WC. Keep it at 4m width. 15 sqm is too much in my opinion - although it’s not really possible to have it too big ;) - but it is a very expensive bathroom. We have just under 8 sqm (3.28×2.45) with a 90×180 bathtub, 90×120 shower, 65 cm sink, WC, and space for a cabinet (fairly behind the door) - I don’t find it feels cramped at all. A room that has also turned out well in practice.