I made my niece a little PVC membrane-reed noisemaker.
You can find a blueprint of it at http://www.geocities.com/tpe123/folkurban/airhorn/index.html
My intention was to tune it to E and just have her drone along on some of my E dorian tunes, but it totally covers up any sound the guitar makes. The perfect gift for a three year old. Loud, noisy, and annoys her mother. =P

Philibuster, who didn't get any instruments, but did get a 25$ gift certificate to the local music store...