Q:

Experiment to capture electrical spark

Today my 8-year-old son comes home from school telling me he learned about lightning rods, and he says, "What if we could capture the electricity from lightning and use it to power stuff?"   I'm aware of the limitations of capturing actual lightning, but I thought an at-home experiment could be fun.   I'd like to help him create something at home that could generate a small electrical spark, and then something else that could capture the energy from that spark.   Problem is, I'm not an electrical engineer and don't know how to design either of these things.   There's a store here in town that sells things like circuit boards and capacitors, and I could borrow a soldering iron from work.   I think if I could just get a materials list of what I will need, I could figure it out from there.   
Can anyone give me some direction for how to accomplish this?   

A:

I would suggest you try building and using a Wimshurst machine

It generates sparks (2 or 3 cm spark length easily reached)
It can light a fluorescent light bulb (just hold nearby while cranking)
Usually includes capacitors to demonstrate storing energy
Is not electrically complicated
Demonstrates generation of static electricity without direct friction
Is mechanically simpler than a Van de Graff generator. 

There are kits and finished machines avaliable, but you can build a Wimshurst machine in your garage workshop from parts you can get from a hardware store.   I found I needed a drill press for some of the parts - hand drilled holes aren't straight enough for longer holes. 
The difficulties in building Wimshurst machine are mostly mechanical. 
You need some kind of bearings for the disks to run on, and you need to cut circles out of a plexiglas sheet.   I used some plastic wheels with bearings for my disks to run on because I could get them cheap.   One of the links below explains how to cut the disks. 
Electrically, you do have to watch for sharp corners on the conductors - the charge "leaks" off through sharp corners, so smooth and sand everything round and use rods for connections as much as possible instead of flat metal. 
You would have the same difficulties when building a Van de Graff generator, and more mechanical problems besides - most Van de Graff generators have a large dome for the charge collector, which can be difficult to make.   The belt for the charge transport is also a problem.   
Electrically, the Van de Graff is even trickier - the voltage can be so much higher that leakage is a much larger problem.   
You also have to deal with powering it.   While you could build a hand cranked Van de Graff generator, most information is about motor powered ones - probably because they take more cranking to build up a usable charge. 
An alternative would be a Kelvin water dropper.   It uses falling water drops to generate a static charge.   I've never built one, so I don't know how well it would do for lighting things up. 

Link to a guy who built a fairly simple Wimshurst machine with detailed instructions
Link to a Wimshurst related question here on stackexchange

This is my Wimshurst machine:

As you can see, it is mechanically fairly crude, but it does work. 
I'll see about making a picture of it flashing a fluorescent lightbulb and post it later. 

For something much simpler:
Scruff across the carpet wearing sneakers while carrying a fluorescent tube.   Walk over to a door and touch one end of the tube to the doorknob and watch the tube flash. 
Weee!