Kids can build them. So I supervised my son to build one...
Video link :
Step 1: What Do We Need ?
1. Old toothbrush
2. pager vibrator
3. 3v battery
4. double side tape
I extracted vibrator from Wii remote. one can buy it too
Step 2: Assembly
Using double sided tape stick vibrator and battery
Put one wire below the battery and other on top. used electric tape to stick it
Step 3: Decorate
My son enjoyed making it
I did this with DC motor with other kids they also liked it