Hi!
If you have had your piggies less than 10 weeks, then your mommy piggy would have come already pregnant but it would be a VERY good idea to double-check the gender of the companion since sows come into season again within hours of giving birth.
Sexing Guide
You can handle the pup as soon as mommy is leaving it to eat; I would wait with the clean until later and you are sure that the baby is suckling and mommy is licking its bum to stimulate the digestive tract, so you are sure that all is as it should be.
You do not need to see a vet unless the baby is not able to lift its head or move around well, or it has problems with ingrown eye lashes and has not open and clear eyes.
Please follow our diet recommendations for pregnant and nursing sows. Babies start nibbling on adult food right from the start but they won't make the big shift until they are in their second week of life. Soon after, mommy will start the gradual weaning process.
Please take the time to read these links here. They should answer pretty much all your questions, but you are welcome to ask any that you still have or that have come up after reading our advice.
Diet recommendations: Please be aware that any extras are already over half covered in a good general diet and that the actual amounts are tiny in proportion. We haven't seen any difference in surprise babies and mothers on a good general diet and those where the pregnancy was known for longer. You can feed fresh grass (dog-pee free please) or more calcium rich leafy greens like kale and spinach during this time in conjuction with a handful of alfalfa hay on top of your normal hay. Give a double sized slice of pepper but otherwise stick to your normal diet, just without portion control as mommy will famished!
Long Term Balanced General And Special Needs Guinea Pig Diets (general diet recommendations)
https://www.theguineapigforum.co.uk/threads/pregnancy-and-nursing-diet.109377/ (pregnancy and nursing extras in addition to a good general diet)
https://www.theguineapigforum.co.uk/threads/after-birth-mother-and-baby-care.109389/ (what to do and to look out for in the first days)
https://www.theguineapigforum.co.uk/threads/first-baby-days-a-video-and-picture-diary.162694/ (this is a diary to show you the development)
https://www.theguineapigforum.co.uk/threads/sexing-separating-baby-boars-and-rehoming-babies.109391/ (sexing, baby boy separation, end of the nursing period and afterwards)
Please bring any mothers and babies indoors into a more stable environment and make sure that they do not overheat. Moms have an overloaded immune system and newborns do not yet have one, nor can they regulate their body temperature well.
Keep mom and her (female) companion together as much as possible unless she is very aggressive to the companion.
Hot Weather Management, Heat Strokes and Fly Strike