(18+ category) I'm 40 years old and I've constructed (with some help from my daughters!) this vibrobot (for those who do not know how they work, vibrobots shake due to the imbalance created purposefully in the shaft of their motors). I chose to call it Brushbrobot because it's a bristlebot, but big.
This is much easier to construct than a small bristlebot and has better performance (bigger pieces, no need for a special vibrating motor, more standard battery, longer autonomy, on-off switch added). It also allows for a rechargeable battery (highly recommended).

Step 1: Materials

Nail brush
9V motor (lower voltage motors could work too)
9V battery (rechargeable recommended)
9v battery clip
Crocodile clip
Piece of wire (any color. I got mine cutting in half the red wire from the battery clip in half, which was long enough)
Unipolar on/off switch

Step 2: Tools

Soldering iron
Solder wire
Wire clipper
Hot glue gun
Glue bar

Step 3: Attach the Wire to the Switch

Solder the wire to one of the switch's legs. If they have holes, you can thread and twist the wire, but keep in mind that the vibration may yank it loose.

Step 4: Attach the Battery Clip to the Switch

Solder the red wire of the battery clip to the other leg of the switch (again, you could twist it if the leg has a hole, but it's better to give it a stronger grip).

Step 5: Attach the Motor

Solder to the motor the free wires from the battery clip and the switch (does not matter which goes where).

Step 6: Attach the Battery

Attach the batery to the battery clip.

Step 7: Glue the Motor and the Battery

Glue the motor and the battery to the top of the brush. Make sure the extreme of the motor´s shaft extends well beyond the edge of the brush.

Step 8: Glue the Switch

Glue the switch to the brush.

Step 9: Attach the Crocodile Clip

Attach the crocodile clip to the motor shaft adding glue on and between its teeth (this is to avoid the clip from being ejected due to the vibration of the shaft as it revolves). If the shaft is wide enough or has a plastic cover, the clip may attach firmly without the need for gluing). BE SURE TO KEEP YOUR FACE AWAY WHEN YOU TURN THE BRUSHBROBOT ON.

It's done!