I think you will be a good pig owner too because you are at least trying to find the right info and do the right thing. I am also the mom of a highly sensitive and gifted kid, she is wonderful with our pets but at the end of the day she's still a kid and that is why I have been basically begging you not to give this as a Christmas morning gift. The excitement of Christmas morning will make any kid forget to be calm!
The other issue that you will find people trying to talk to you about is getting the pig from the pet store. You won't find many people here that will support you if you choose to get the pig from a petstore instead of adopting. Many people get their first pigs at petstores before they know any better, but once you know better it makes no sense to get them from a petstore. It dosen't matter that you are getting the pigs for free and from your friend who owns the petstore. The fact is that they are still coming from a breeder of some sort and your friend is paying the breeder for them. There are some really great threads here...after I read them when I got my first pig at the petstore I was horrified. I have since then gotten 2 more pigs and both of them were adopted. I will never ever again buy any animal from a petstore.
These are some of the threads to read
http://www.guineapigcages.com/forum/...r-threads.html http://www.guineapigcages.com/forum/...e-breeder.html
I really don't want you to think that I am saying you will be a bad owner, the fact that you came here looking for information shows that you mean well and that is more than many others who come here. You have also shown that you are not expecting your kids to care for the pigs on their own and that's wonderful. Many parents get small animals for their kids and then get upset when the kids do not take care of them. I have a feeling that you would not be like that.
If you would like help trying to find rescue pigs in your area then let us know, people here and at guinelynx.com are excellent and finding rescue pigs. If you can wait a few weeks and are willing to really look then I am confident that you will not have to get them from the petstore.