I would move the ‘kids’ sofa further towards the door and put space behind it.
I’d put a bookshelf all along the wall behind the moved sofa. Lots of books, pictures etc on the shelves
I’d have the tv taken off the wall and put on the TV cabinet in front. I’d then put pictures (with Velcro strips) on that wall.
I’d move the sofa you are on further into the room.
I’d put a warm coloured rug down (possibly hot pink or raspberry coloured to tone with the curtains and cabinet)
I’d put a coffee table on the rug
I’d get a floor lamp and 2 tables lamps - one of those would be on the bookshelves and the other behind the sofa you’re sitting on
I’d change the ceiling light to tone with the rug / curtains and lower it
I’d have a small occasional table near the windows or use one of the other cabinets
I’d put radiator covers (you can buy flat pack ones) over the radiators and paint them navy
I’d buy lots of plants and have green, pink and navy cushions on the sofa (different shades, none of them actually matching)
The kids would not be allowed to ‘dominate’ the rooms layout. (I use dominate loosely but their den would need a new home). I’d get a couple of bean bags for them.