Denis Wick create back pressure that students have to play against. I have seen this work to boost full brass section sounds in HS groups before. But if they play into pressure it can create strained sounds.
Another option is more expensive but probably better. Using a more free blowing mute like TrumCor mutes that play nearly as free as no mute but making your kids play FFF will do just about the same thing but can avoid the strained sounds. But again it costs like twice as much.