Room-to-room air flow without passing through noise?

I have a basement office, which is pretty nice. I have one ventilation duct mounted high on wall next to my door, but no returns in the room itself. We have a few more vents sprinkled around the ceiling of our semi-finished basement/homeschool room/kids play room. I've noticed that if I keep my door open, the kids room stays much warmer while mine stays comfortable. I can't leave the door open or else the kids wander in and interrupt my work. I've been thinking of creating a duct to allow air to flow from my office to the kids room, but I don't want to transfer the noise they create. I almost need a muffler plumbed sideways in my wall. Any ideas on how to let air flow freely between two rooms without letting soundwaves through?

One idea I had was to use a 6" piece of PVC pipe laid sideways and install some baffles in it. Ugly, but then again so is the quality of my office "finishing" level.

What you want to do is provide a path for air without providing a direct line of sight for sound. When I need to provide return air for sound sensitive areas I usually provide a U or Z shaped duct so that the air can get through while blocking the sound. Your 6" PVC idea should work but put an elbow on each end turned up.

Cut two holes in the wall to fit transfer grilles (or any vent from a store). One hole on your side of the wall at one elevation and the other on the kids side of the wall at a different elevation. Slide in some duct board from your local home store to line the space between the studs to make a 'z' shaped duct in the wall (like what tomtomg356 said). Get some good tape meant for duct board. Try to get it enclosed so its not open to the rest of the wall and it will help with the noise. Install the grilles.

Try shutting off the vent in the office? Should redirect the warm air to the other ducts.

Insulated duct. It's not cheap but it's used in TV studios and such.

Make your own? Duct, plus roxul sound insulation glued in?

I'd start with a $40 louvered closet door. If one can keep my ancient washing machine quiet then I think keeping a little intermittent kid noise shouldn't be an issue.

One of these and a half door?