Ikea cabinets would work.

What is your goal? Blocking the view? Sound reduction?

Assuming you are looking to enclose the space I would do arched French doors to fill the arch.

Maybe a double barn door in the same finish as the front door? You could keep it closed when you are trying to hide the mess from company (I'm guessing that's the goal here) and open it when that it's an issue. This will save having to remodel when you want to revert it in the future.

@apple_pie_order: the goal is to (1) utilize the space as if it was enclosed to add a third full wall, (2) only have one point of entry in the room as my kids are young

@holly6482: my husband had mentioned barn doors!

@LisaCaudillDesigns - those are gorgeous!

@partim: any specific brand/type you recommend?!?

You could put them on the other side of your entry as well where the are is brought in to fit regular French doors.

Glass options with ones are beautiful but for a kids playroom just felt the solid door would be best.

What a lovely idea for your children.
As suggested have doors made to mimic the front entrance. I would have the glass frosted to allow light but provide privacy.
As an alternative why not have bookshelves built in to the arched opening? The only picture I could find had a secret door option ( see below) but basic shelving would work and provide storage for your playroom. Leave the arch at the top, please, to echo the remaining doorway style and shape.

@SuzannePeacock: I love the bookcase door idea, I’m going to have to look into that - thank you!

• Turn it into a puppet stage à la Sound of Music.
• Make it a kid-scale theater set.
• Build a castle.
• String hammocks for quiet reading time.
• Create a climbing wall.

I have a Murphy door (the bookcase type, above) on my entry hall closet and love it. They do make in double width though you’d need custom millwork to fill the arch above.

You may want to reconsider before doing anything too permanent or expensive. As you have it now, the hallway extends the size of the room and is available as play area/running around area too. We don't know the layout of your house and how it relates to this room, but at some point you may want your children to be able to run around in the hallway, run back into the room etc. Depends on their ages but they grow and change fast, so you may want to keep the ability to put the room back to the original configuration easily.

If you want to block the view of the room from the front hallway, it could be as simple as putting curtains (portieres) across the opening.

The theater "set" and/or playhouse I described above, would be made with painted fabric. You could have one on the back wall for the background, and one in that archway for a theater curtain. Dress up "costumes" from clothes and fabrics from Goodwill. Or, heck, puppets.

@partim: good point about them running around, right now they are 3 and 5 months and we plan on Being in this house a long time

@tangerinedoor: love the creative ideas! I wanted a stage area for my 3 year old as she is very dramatic and loves to sing songs

Crazy idea - would a large hall tree make sense for the entry way? We don’t want people to have shoes i the house? This could cover the entry archway and on the other side in the playroom have a couch against it to make it a complete wall space

Great idea...but even better if you add a bench..for guests to sit down and remove shoes