I assume the tall shelf is bolted to the wall? I would add a nice shallow open basket to hold toys that you can rotate every week or so. Agree with KR's specific bookshelf example - it is nice when they can see the whole book instead of just the spine. What about pictures of the whole family, pictures of grandparents?

Is painting an option?

I would get a warm rug. some color down there will change the whole room! Maybe some more more colorful art with darker frames.

what a beautiful picture perfect room! To add some warmth to the nursery I would add drapes but how much more polished can you get. If you mean warmth for a toddler add some stuffed animals, toys, a rocker, blankets you know they would love to drag around with.

I like the idea of repainting but I’d do a lighter blue than the ones above

warm and polished are not really compatible goals. it's elegant and refined and looks like no real kid will ever live there. he's past the age when he needs to see a lot of color already, but still, some might add fun?

This room is polished if you mean re polished by adding paint I would choose a darker gray like BM Collingwood or BM Gray Owl which will still keep this room elegant and plush.

Sorry but that is IMO not a childs room at all except for the crib. That tall bookcase needs to go for sure .It won’t be long until he is in a bed so make sure whatever you do will handle at least a twin bed. This just looks like an adult guest room so IMO start thinking like a child . No table lamps , I think the crib looks like afterthought . Wall paper would be fun or just decals that can change as he ages . A fun rug the low bookcase for sure but honestly this space does not look very large and once a real bed is in there how much space will there be? Maybe post a to scale plan to give me at least a better idea of the space.