This summer during the Maker Faire Moscow (https://moscow.makerfaire.com), I conducted a workshop with children. The main goal was to motivate them to make something with their hands. It was also a good pretext to make them understand the very basis of electricity and also some mechanical principles. So I designed this electric wooden bike keeping in mind these requirements:

Children age was between 6 and 12 years old
No tools needed to assemble (a plier helps)
Available time around 15 minutes
Customizable
Replaceable parts (standardized)

Step 1: Tools and Material

Tools

Laser cutter
Plier
Metal saw

Material

Plywood 3mm
White glue (wood glue)
DC Motor 3V (Velleman, MOT1, https://www.velleman.eu/products/view/?id=375872)
Battery box with switch (KLS electronic co, KLS5-805-B, http://www.klsele.com/products/connectors/Battery...

Two AA batteries
Rubber band (loop 18 cm)
Brass tube (4mm outside diameter, 3mm inside diameter, length 20mm)
1 screw M3 x 50 mm
1 screw M3 x 20 mm
4 nuts M3

Step 2: Cut the Parts

You can download the files and cut the parts with a laser cutter. You also need to cut the brass tube into two 4mm and one 8 mm parts. I used my mini table saw (proxxon KS 115).

Step 3: Assemble the Frame

Assemble the saddle with the two plates
Put the saddle on the two frame parts
Add the motor and battery
Secure the motor with the small lock
Gently press the pulley on the motor axis
Connect the electrical wires. (make a hook at the wire end, pass through the motor pins and squeeze it with the plier) (test where the red and the black wire go)
Add the radiator and the headlight

Step 4: Assemble the Fork

Press the 8mm tube into the wheel with the 4mm hole (use the plier to squeeze or hit)
Take the M3 x 20 mm screw and insert the first fork side, the front wheel, the second fork side then a nut (do not tighten it)
Insert the assembled fork and then the handlebar

Step 5: Assemble the Back Wheels

Press the two 4mm brass tubes into the rear holes
On the M3 x 50mm, insert two identical big wheels then a nut (tighten it)
Pass through the rear axis and secure with a nut (do not tighten the nut, leave some slack)
Add one big wheel, the smaller one, and the last big one. Secure with a nut. (This one has to be tighten)