Instead of the solid grey, you can go for sketches in grey with flashes of mustard/ yellow. Or, look up these links for wallpaper ideas https://goo.gl/images/OrCtY1 https://goo.gl/images/0ZpAmU

A rug with a horizontal pattern could help along with a false ceiling above in which you can install a line of recessed lights. The tiles and border on the walls suggest that this is a passage in a shared washroom space like a health club. It looks a bit cold for that reason. So hang a lot of warm framed prints to make this space more inviting.

I can see a dresser area outside the bathroom in the floor plan and a separate wardrobe area as well. You can make an exclusive wardrobe and dresser area for your daughter just outside the bathroom. The wardrobe space can accomadate a long study table with wall mount bookshelf and a mix of open and closed storage. On the same wall you can make a sleek wardrobe for your son. Trundle beds are also quite in these days, you can place a trundle instead of a regular bed. Place the bed against the same wall as shown in the floor plan but tucked away in the corner. On the opposite wall you can get a nice kid friendly theme on the wall and create a small seating. Use all white furniture and add pops of colour through curtains and bedding

I select these colours with the help of other houzzer and expert professional advice and discussion. I also got help from colour paint catalogue. Is it looking good or not? Is there any problem with these colours and their combination. Please guide me in this regard.