I have literally done 100's of school shows as part of being a supply teacher. Often a music teacher who is sick just leaves a video for the kids and I couldn't stand it anymore. I decided to bring my bass. This way I also get to be paid to practice in front of people.
I tell them to hold any questions until a question period. If I don't there is a constant stream of interruptions.
Since most kids don't consciously listen to classical music, I relate it to what they do know..TV, movies, video games.
Here's the basic plan of my show:
I. Construction of the bass: the different woods and parts of the bass and bow/rosin. I talk about why different woods are used.
Question period
II. Role of the bass in an orchestra: I sing a melody and play the bass part - ex a few bars of Oh Canada or In the Jungle, etc. Explain how each instrument contributes to the whole.
III. Where you hear a bass: in the background of TV shows and movies; usually when there is something ominous going to happen (tremolo low notes; I sometimes play the first half of the first page of Mahler #2 to represent waves crashing against a lifeboat. Also, In the Hall of the Mountain King or passages from Beethoven #5 Mvt 3 works well here, too.) Or, the bad guy shows up (Wolf theme from Peter and the Wolf, Darth Vader theme and JAWS (have the kids close their eyes and imagine they are swimming in the ocean)- start low and go up octaves until gulp! You'll get requests to do this again!
Question Period
IV Actual pieces: Here's your chance to actually play a whole piece of music. I play Bach Bourree #3, O Danny Boy, Bottesini A minor Concert Mvt 1 with out cadenza, Monti's Czardas (just the fast part, no repeats) I have a few Music Minus One recordings on CD that I play with these.
V Actual Piece part 2: I put down the bow and explain the bass was used in Jazz and early rock n' roll. I play The Pink Panther and sing Hound Dog while accompanying myself.
Question period
VI Student try bass: Explain they are not allowed to touch the hair. Pick a keener who isn't a goof (very important). Ask him/her their name then quickly show them how to hold the bow. It doesn't matter how "correct" it is, as long as they don't drop the bow!
I stand to the left of the bass and hold on to the block so it doesn't fall. Have the kid saw the E-string while you take their left hand and show them how to play the JAWS theme.
Then say, "A big round of applause for ______ playing JAWS!" (kids go crazy!)
Have person A pick person B (if girl, have her pick a boy and vice versa)
Person B also plays JAWS
Person C just pizz's the D and A strings them lead crowd into singing Row, Row, Row Your Boat or Itsy Bitsy Spider.
Person D pizz's DDDD, GGGG, DDDD, AAAA repeat endlessly, have crowd sing In The Jungle
VII End with a flashy piece: I play and sing Old MacDonald Had a farm and make animal noises with my bass (mouse - short string on extension; Cat - a high note on G string with a short slide downward; Cow - start around B on the E string, slide up a bit then down; Horse - finger taps on the body to imitate the hooves, get louder then softer and turn head from left to right to imitate the Doppler effect of a horse running by; Seagulls - start way up on the G string and place hand gently on the string, run hand down the string playing a long bow so just the harmonics go EE EEE EEE EEE; Wolf - artificial harmonic way up the D string (ex. thumb on D, note closed, third finger on the A harmonic above) and make a small slide down; Shark - JAWS)
Hope this helps .