Not sure what you're looking for...Building solar panels involves soldering, I wouldn't recommend for a 4th grader.
If it's to demonstrate solar, you could, pickup a small panel and some NiMH or NiCD batteries to charge and some cheap electronic gadgets. I did this for my nephew. just used bolts for terminals, dollar store fans, and short string of LED 'Christmas lights that ran off battery pack...
If it is indeed building solar panels, I would suggest getting some 'tabbed' solar cells these will already have the thin tinned leads soldered to the back of the cells. They can be found on eBay or Amazon. For a small demonstration project, I might suggest creating a 5 volt charging station and again use 4 NiCD or NiMH batteries. Many things run on 5 volt USB these days and you can butcher an old tower for a panel type usb outlet.
Soldering together raw solar cells that are more fragile than a potato chip with a 700'F soldering pen and lead solder.
I started soldering when I was in 5th grade, only burned my self good once. Then you learn.
Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.
Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.