The larger distances betweens walls will immediately affect the physical intensity of sound of computer sounds. Put comfy furniture in the middle of the room as a discussion area. Use a rug in the room and hang banners on those hard walls. Bodies will absorb sound too. If you have a table in the center of your room, put a heavy skirt around it.
Every room is a little different.
Volume is reduced when sound is not aimed directly at you. Think of the sound as a cone coming out from the speakers. Putting speakers behind the monitor, which means further from the kids, creates a larger sound dispersal area unimpeded by any deflection or absorption. That only forces the kids to turn up the volume. Bring them up close and in front of the kids.