A bit vague . Art driven you will need the supplies that can be used by those ages and a nice accessible place to store all those . A bigger table since they will all want a space at the same time. Since it appears to not be in the main part of the house on disply some nice open storage for toys and books . A seating space and trully not kid size . A washable rug and be prepared to change things often as they age. I would not have the 1 yr old in the space right now he will be more trouble than you can imagine . I ado not like kid size stuff they grow way to fast so anice long table along a wall with chairs for arts and crafts . A sofa or 2 smaller scaled adult type chairs for seating and lots of reachable storage all tethered to the wall Ikea is a great place to shop for this stuff IMO. I see a TV so make sure the remote has a home too.Once the little guy is 2 he can join the fun but the girls will not be happy at the beginning , Paint the walls a nice neutral and use a big chalk board for wall art . In fact you can paint a whole wall with chalkboard paint if it seems like a good plan for your kids.

Would give some thought to exactly what you want to accommodate in the room - seating, tables, chalk or white boards, etc. And storage! I see there is a closet. Is it sufficient? Do you need shelving? I can see shelving/storage all along the shorter wall. Would suggest you search for inspiration rooms/photos and use those as a guide. Good luck!

Hard to tell the size from photos, especially with the distorted lens. Definitely wouldn't block the window with cube storage. TV is mounted way too high for kids.

You can get cute cube storage baskets from 3 sprouts. They fit in IKEA's cube storage. Not sure how big your cubes are.

We bought this art table and it has been great. It is kid sized but I can sit at it just fine, so I think it will last until my kid is not all that interested in art any more. Or if she IS still interested in 5 years we'll start buying her better stuff.

https://guidecraft.com/products/martha-stewart-living-and-learning-kids-art-table-and-stool-set?variant=43968389218559

Your table and chairs don't match your rug. What does "art-driven" mean?

Full of inspiring art on the walls? If so, start looking for art. I like prints by artists, rather than kiddie stuff like cartoons or Disney.

Do you mean a space where your kids will do lots of art? If so, put a picture rail along the back wall or some other system for hanging their art. Don't put up one small cork board. You have a lot of blank wall and kids produce a lot of art. A picture rail or cork tiles all across the top of the wall will give you lots of space for hanging and provide some noise dampening. You don't want a system designed for framed pictures. Something that will work with clips or push pins, so you can remove an older work and hang up the latest pretty quickly.

If this is your vision, you want some flooring that can take paint spills and ground-in play dough, meaning remove that rug.

Who said anything about a cork board ? I do like the idea od the rail to hold art it is a great idea. My kids loved the chalk board for stuff easily erased . We do need to get some answers fro the OP to know what is really needed .

Perhaps take a moment to make a list of the things you want in the room, then look at playroom ideas on here, and make an ideabook. Here are a few of the playroom and kids rooms we have completed for clients. Please take note of the storage options as well.

Highland Park Phase 2 · More Info

Hockaday Neighborhood · More Info

Hockaday Neighborhood · More Info

University Park · More Info

If you're looking to perhaps make a fun space for your kids. You should make a list of all the things you want them to be able to do, and furniture you'd need in the space. Then make an ideabook on here and look at different kid friendly spaces. Below is just a few images that might be able to help:

Relaxed Family Home · More Info

Relaxed Family Home · More Info

Relaxed Family Home · More Info

Good advice already - if it were me, i would remove the closet door and hang fabulous curtains there and retrofit the closet to hold tons of supplies so the kids can easily access what they want without dealing with the door (think about what should be reachable and what should be higher up) - I woukd also build a long line of closed storage along the short wall and mount a TV on that wall (but in the corner, not the middle) and would get those shutters open to let in some natural light —