Not all of the responses below are accurate...please research from a reliable souce before getting a Guinea pig.
A good web site is cavy corner. http://www.cavy-corner.0catch.com/index.html
We picked up two guinea pigs when my daughter was 2...
my suggestions, don't put them in the child’s room. Have them at a level so the children can look at them and they won't be temped to climb and pull the cage down. And supervise all contact.
They need fresh food and water every day. They need ruffage, fresh veggies & Timothy hay, they don't need special vitamin C treatments, just an orange slice once in a while. I have two piggies in a small cage (from Petco for $60)so I clean the cage every two days, lined w/ newspaper, a layer of cedar (to keep down smells and soak urine) then our old shredded documents or shredded newspaper.
Piggies are social animals so it is suggested to have two...but that also means twice the litter cleaning. They also need regular handling and exercise, I layout on old rug and sit w/ them while they run around and so my daughter can pet them-teaching her ‘soft hands’. The more you handle them the easier floor time is. My piggies know to stay on the specific rug so I don’t have to chase them around. They will chew so be careful they don’t get around electrical cords. We handle them about 20 minutes at a time to prevent piddles on the rug, they pee as much as a 8 week old small breed puppy which why they need frequent cage cleaning.
They can swim, and you can bathe them with mild soap-I use my baby soap. They also need toenails trimmed every other month which can be done w/ cat or puppy nail trimmers.
They have been great for my family. My daughter has learned to care for her own pet. She’s learned to be gentle. Also I like that they are safe and contained and don’t get into things like a dog or cat. I really like the fact that I can control the contact. I know and my child won’t get bit, scratched, or knocked over.
You can rescue a piggy at Petfinder.com or contact a 4-H child that raises them as a project. I would not suggest supporting Pet stores. Both of our piggies are rescues.
Good Luck!