@Dontsparethehorses just while I'm lurking waiting for these *piglets to make an appearance ..
*proper name is "pups" but piglets is cuter
YY to what Guppy said re allergens . And hay is a huge allergenic too but you cannot get round that . They need unlimited hay 24/7 . In Summer or if one had an eye injury we gave hay cookies (less messy) or hay packed into loo roll tubes . But you cannot avoid it .
And the coats - we had Smooth+Abby (rosettes) which was fine , then Rex (DD was allergic) another smooth , a crested smooth Himalayan(apparantly quite rare 
) , a Teddy (more allergic) another smooth and a long coated .
The more complex the piggie the more potential health issues .
Abbys have shorter muzzles so higher risk of breathing problems (not flat faced like the dogs but shorter ) higher risk of cataracts , ours had a fatty eye (white skin lump in the eyelid)
The Rex was 1.4kg , massive boar , thick claws which are tougher to cut .
Teddy and Swiss have drier skin. And if you get a longer coat you need to brush and comb them and keep the fur clean and unmatted (or cut it for the piggies comfort)
A couple or more good solid smooths (Solid as in No Frills not colour 
. A neutered boar and a couple of sows is a nice group . Sows can fight , boars can fight . There's no ideal .. I found sows were messier . DD found her boars were friendlier .
But if you want boars only get 2 . Trios are hard work to maintain.
If you get a mixed sex group , only 1 boar .
They need a lot of space , preferably one level . They can climb ramps but prefer not to . Each piggie must be able to get out of a sleeping or hidey box without being trapped .
They are vunerable to damp cold heat draughts .
They are gentle and very rarely bite but they CAN bite and in 99.9% of cases it is the humans fault . (My rare crested Himmy was a gnawer but a child would say she biiiiiit me )
They will let you know if they want a pee , you get to know the signs , but poo with abandon.
Children have to respect and handle them carefully , a drop could kill them.
They need to know what to feed and what not to feed . Lots of things can make them ill and they cannot vomit .
They need Vit C (its in the pellets and veg too)
They are the untidiest , noisiest , greediest little mammals but so lovely , and hard work .They are also As Thick As Mince ( I know it's not nice but it is true , )
They need to be in a group or pair , so one dies and you need a new cagemate .
Our pigs were all from Rescue and characters .
My DD got rashes on her face from the 2 coarse coats (we didn't have them at the same time) she wouldn't let me have her boar she put up with the rash!
Baby guinea-pigs are the cutest ever - fur, claws,open eyes , teeth, can waddle about within hours .
Now just waiting for PicklePig to announce the arrival