This is made of tatami, tatami+locker, with a wardrobe next to it to increase storage. Next to it are tables and chairs, and bookshelves. Although there is not much space, there is everything. The children's room has bay windows, which can reduce the area occupied by the "bedroom", because the bay windows can be set as desks, and only one chair is needed. Under the condition of not dismantling the bay window, a "desk" with a certain thickness can be added above the windowsill in whole or in part to reach the appropriate height of the desk, or drawer-type or cabinet-type, depending on the height of the bay window sill.
The seat should be adjustable: children are shorter than adults, and using adult tables and chairs will affect the sitting posture. Moreover, children's bodies grow fast, and tables and chairs with fixed heights will soon be inappropriate. There are many companies that make custom furniture on the market now. I suggest you go to several famous local shops, and then invite designers to take measurements and give you 3D renderings. Don't worry, these services are free, and it doesn't matter if you don't cooperate.
In the children's room or expansion point, any big items at home should be added. The most basic thing is to plan in advance where to put such things. As far as children's rooms are concerned, when it comes to desks, it refers to other furniture, such as beds and wardrobes. When these large items are taken into account at the same time, we should first look at the children's daily habits, and then put them locally through reasonable design, so as to ensure that children can use the desk conveniently.