What's on the other side of the room?

On the other side is his desk and study nook area. The window there is quite wide so we couldn't really use it for wardrobe space.

How good is your sound insulation? I wouldn’t put a bed against a wall with a toilet on the other side, also torn by a bed against the lounge room wall though! If you are at all interested in ‘energy’ and feng shui you would also avoid the toilet wall for the bed. ;o)

Dimensions and sill height of window would help

Is the study nook separated from the room by full height dividing wall, if so, thinking building in full height wardrobe cupboards on both sides ie, backing onto the study nook. Put the bed under the window at back of house, not necessarily centred.

Or if they are not full height and since ur renovating, remove them, put bed way under the window, obvs dep on window height, wardrobe where blue all way along that wall beside the new bed place, study goes where red now shaded.

I think the other question is where would you out his bed? Beside the wall so he has lots of space to play in the middle of the room? Or is he older and would prefer to have access to both sides of the bed?
I'd try to keep the square shape to the room rather than running a wardrobe down one wall and the bed opposite making it longer and thinner.

Definitely blue shaded space. You don't want the bed on that wall as it would be very exposed to the door. Not nice having bedhead against toilet but a good, wide bedhead or even bedhead storage might fix that. Similarly, the bed could go in front of study nook entry if a solid enough bedhead were used.

I am going to disagree with everyone else. Go with the red. Reasons:

It will block bathroom noises. Additionally I am going to suggest that at the same time, you move the door to the room in to square the room with the outside of the new wardrobe. Also, while you are doing
the reno, (and enough cash hopefully) make the wardrobe about 600mm smaller in length to create a new hallway cupboard for extra broom or storage space.

Additional to that, remove those two half walls over by the window area and place the bed on the wall opposite the lounge. The entire lounge wall is then freed up, to create a lovely area for play. You could create a built in desk, toy store and even a climbing wall or some other adventure space if you were so inclined.

By getting rid of those two walls, you will be astounded by just how big that room really is.

I can see it being a wonderful guest room too, in years to come.

How wide is the wall to window and wall. If it is 600mm I would put the wardrobe on either side in the sunroof area and if you could push the wall back to extend 650 it would be perfect

I vote with lynda. Walking into the room into the side of the blue wardrobe would be very unpleasant