Hi, and welcome to the forums, I am sure your son will love the Ugobe Pleo, I am a grown Mother with many Ugobes and they are wonderful. Because of his age, be sure to supervise him carefully though. They do reccomend ags 8+ but with supervision he should be fine. As for updating him, first I would say,why not just enjoy the orginal operating system and let him enjoy that till the battery runs out, it does have it's own unique sounds.( when you rub the Pleo under the chin, it souonds similiar to a coyote or wolf howling and is cute.)

The second stage is 1.1, which a lot or vast majority of Pleos at least on Ebay will be running, This has it's own unique sounds as well, and it is my own personal favorite. The last operating or latest operating system is the current, 2.0 which I think a young child would have or could have some trouble getting used to. I think there are enouogh members here on the forum that could explain that better to you than me, as I only have one of my many Pleos running 2.0. It takes more battery cycles to get rid of some of the glitches or problems with 2.0, but once they are worked out, it is a great operating system and has lots of great tricks that Pleo can do.
As for putting one SD card into Pleo, turning him on for a few moments and then turning him off, putting the next operating system in, etc, that is not neccesary to do, Let's say you just wanted to go straight to 2.0 . All you would need to do is to have the SD card copied with the 2.0 operating system on it, and then follow the directions for installing it onto Pleo, and put it directly into Pleo. You can go straight from 1.0 to 2.0 if you want and do not need to do 1.1 first, It is up to you to do which ever operating system you want, but why not enjoy each system for at least one battery cycle and get familiar with what Pleo can do. ? There is no hurry to have to update him unless you want to. And you can also save money on SD cards, by just using one and when done with the 1.1 and wanting to try the 2.0, just erase the files on the sd card and update with 2.0 on the same SD card, as a blank !
One other word of caution, esp if this is for a Christmas present. If this is a Pleo bought on ebay and an Ugobe, a 2007 Model . Not used or hatched, more than likely and other members will tell you the same thing, 99% of the time, the original battery sitting in the box all this time, is not going to hold a charge an will be dead or perhaps let Pleo run for a few minutes at most. I have bought at least a dozen Pleos on ebay and they all needed new batteries. I only tell you this so there won't be an unhappy child opening up Pleo and not h aving him work. I do sell batteries, the Ucube egg batteries to members here on the forum and they will give you twice as long as the usual batteries, 2 hrs compared to just one. You can also buy batteries directly from PleoWorld, but they will cost you more than myne, but they are available and work fine also. You and your son are in for a treat with Pleo. Welcome again to the forums.
RedwoodsMama and the Pelo Clan of the Redwoods