Children's room and bedroom - What size is recommended?

I have hated my 11sqm room since I was 14. I wanted a 1.40m bed and a sofa. That was one of the main reasons why I moved out immediately when I was 18.

Since we have a few more children than usual, there are only 12 to 13 sqm of children's room per child. However, there will be a large plot with a garden house for the older children and hopefully also a covered terrace for a pool table. And of course, playing is allowed in the living room as well. At the moment, we have 10-12 sqm per children's room, which actually works well. However, our children have relatively few belongings. If the room is not too cluttered, 10 sqm can also be arranged as a cozy retreat. A 1.40 m bed is of course not possible. But there are more important things. If we had a bigger budget, there would have been bigger rooms. But 4000 more per child is 20,000 for us. We rather saved that money and invested it in a caravan for everyone. That makes the children happy too. And you can't have it all.

There is no standard size for a children's room.

They must be well furnished, bright on the chocolate side.
It depends on the size of the house and the number of rooms. What other play and recreational possibilities are there.
Arifas, your "small" children's rooms are easier to furnish than the large ones in another thread. What use are the pure square meters if it becomes an art to place the wardrobe properly?