A cozy rug would look nice and keep your children without hurting knees.

A table would also look nice. And a TV for them. Also more color.

I agree a rug first then look at IKEA storage systems like BESTA

Some of our children's art on the wall, Ikea have frames dirt chap.

A tv on the wall would prevent injuries.

Is this a basement? Or the main floor? Is this an ideal location for your playroom? Is there another space to use? I’m thinking if this is the main floor I would prefer it to be in a more hidden spot as opposed to coming down the steps into this space. Anyways I think built ins on at least one wall. Or a closet a rug and a small cute couch

Its a main floor, and I dont have other spot

Here is a playroom/kids space we designed. Perhaps sharing this will allow you to move forward. Take note of the rug, table, chairs, and storage.

Farmhouse Aesthetic Residence: Kids · More Info

Farmhouse Aesthetic Residence: Kids · More Info

Some shelves on the wall would look good. And a book shelves with boxes from Ikea to hold movies and music disc.

2"x7" Reclaimed, Floating Shelf, Open Shelving, Easy Hang, 48' · More Info

This cost $148 on Houzz.

This box would look good in the floating shelf.

DRAGAN Box, set of 3, bamboo, 9 ¼x6 ½x5 ½" - IKEA

It's bamboo.

Also a colorful wall would look nice.

Maybe their favorite color would look nice.

For girls pink looks good.

For boys blue is good.

Kids love to play on rugs. A nice thick one will allow for gymnastics and rough housing. You can also add in a table (regular adult height) for crafts and games unless you already have a craft room. Our kids spend so much time at our "school table", I have the markers in a big caddy and a big stack of paper out at all times. Art is much more fun when you have a set up place for it.

I agree with @isabellagracepan.

A colorful would look nice.