Possible option for "framing" the window in the play area with functional storage, would also add pillows to bench area since window is not as low, and add crown molding to make it appear more built-in
Simple built-ins to create a mudroom or storage anywhere from a kids room to a laundry room by adding shelves or a deeper bench for sitting. Or instead of custom, buy two thrify store bookcases and paint them, bolt them to your wall and add wainscotting between them. Then pick up a thift store bench and cut it to fit. Add the hooks and you're set. - interiors-designed.com
How to Upholster a Bench- Step by Step This was such a fun project, and now I want to upholster or reupholster everything! So fun to make something that looks so great, and it wasn’t even hard. We did some playroom benches with baskets for toy storage.