My three granddaughters have two guinea pigs (between them). They love them dearly. And they have been good at socializing them - taking them out every day and playing with them so that the little critters are not afraid of people.
I am so glad that they don't treat their pets as "disposable" just because they're small; these GPs aren't pampered, but they're truly loved and cared for.
There is guinea pig food in the pet stores, but if I were you, I'd talk to a vet first (yes, there are vets who take care of these critters). We had a sad situation when my younger daughter had a parakeet - we bought the line, which we had read in books, that parakeets live on bird seed, with fruits and veggies as a treat, when in actuality it was the other way round. The poor bird could have lived quite a while longer if we had realized what he needed. While you're talking to your vet, ask about diseases; it's good to know in advance.
Because GPs are part of the rodent family, they MUST always have safe things to gnaw on all the time. Their teeth grow quickly and, if they can't keep them working, they grow so large the animals can't eat.
They do make noises, which are not too irrititating except sometimes in the middle of the night. And they are messy as well as smelly (as all rodent types are), so you will be cleaning the area around the GP's cage as well as the cage itself.
The little guys have personalities and temperaments. One of my grand-GPs lets us know very clearly when he's stressed or afraid about anything! His owner has taught him to go through a maze she has made, and she also bought him one of those balls that he can go into and roll around the room (with strict supervision).
Here's a place to start (but follow it up with a talk with a real vet):
http://www.aspca.org/pet-care/small-pet-care/guinea-pig-c...