GPU miner is typically a build yourself rig Using AMD graphics cards (GPU's) as the source of computing power for mining.  Buy the components (mobo, HD, CPU, Ram, graphics cards, PSU, OS etc) mash them all together in a milk crate or open air custom frame/case download a miner program set up a pool account and start mining.  Unfortunately it really isn't economically sound right now to purchase and set up GPU rigs for BTC.  What a lot of people are doing is shifting their GPU rigs or building new ones to mine alt coins (which are usually similar to BTC in that they are digital currencies but also differ in some ways).  Litecoin (LTC) is the second largest coin and the largest alt coin currently (at least according to market cap).

LTC uses a different algorithm than BTC and at present time no known FPGA or ASIC miners exist for LTC (although there are reports FPGA's are being designed for LTC).

I built a GPU rig a few months ago and have been happily mining away LTC.  I have traded some of the mined LTC for BTC through an exchange and have kept some LTC as a bit of a bullish bet on the coin itself!

I wish my son was old enough to have helped me build my rig it would have been great father son time!  The bonus for your son is if you spend a few extra bucks on some of the components, having a PC with a few GPU's would make a pretty sick gaming rig!  You guys can game, learn/teach him how to build a computer from just the components, mine a digital currency and convert to BTC learning some trading practices along the way.  You won't make millions but the rig should pay for itself eventually!

What would you pay for a jalapeño PRE-order?
This farm you have a pic of looks expensive, real-estate consuming, and less profitable?!?

Well, IMO the times where you can make some serious profit with mining at home are over. It is becoming a serious business. But thats only normal. Every marked becomes more competitive as it grows and that the Small Private Businesses die out is also normal when a marked grows.

Don't expect to make some serious money mining. But if you want to get in as a father son project where you can spend time with you son and build something together have fun and maybe puts out a little bit of money, I would say buy some usb miners.

You can setup a miner like this one:

http://i.imgur.com/BJCe9a0.jpg

At first, get it working some how.

Next project could be to get a dedicated Raspberry Pi running for it, so you don't need you PC running.

At next build a nice housing.

Improve cooling to make it more silent.

Always something to work on and have fun together and maybe even a little bit of profit.