Guinea-Pigs are the loveliest animals -IMO the best of the furries.
Before you start measuring up Hog Space though, make sure your DS is completely on board (or you will end up doing all the work) . You'll end up doing most of it anyway .
We have two boars (my DD wanted a pet and as I'd had GPs from 9yo-22yo, we went for pigs) . She was adamant she wanted a boar so that was a learning curve for me. My first pig was a boy (a sad little case, bullied by his stroppy mate) the rest girls.
My DS wanted one of the pigs (we got adult brothers from Rescue) but he did nothing for his pig, so very quickly he became mine - which was originally the plan.
Space wise, ours had a 4'x2' indoor night cage and they hated it. Far too small, even though it was just for sleeping in.
They have my DC old wooden Playhouse, which indoors has a floorspace of over 6'x6' (I think i's nearer to 7' not measured it for ages), with a big haybox.
We have a window (reinforced with metal grid and mesh in the 'inner frame' ) that comes out , three others that don't, so plenty light.
A fan (oh yes 
) for summer. Heatstroke can kill them
A radiator for winter (they are indoors at night, out in winter in their Pighouse)
A rabbit run (84"x48") for summer on grass.
My two boars at the moment are the older boar and the new pig (7 months) we knew the cage just wouldn't do. So they have the small bedroom for their run ( it's about 5'x3' with an extra bit in the bay window) but no cover , we don't have cats.
So, if you have the space. Your DS and you are on board.
You have the room for hay (and don't mind the smell of hay and the fact it gets everywhere )
And they pooh - but it's inoffensive pooh.
Read up on their health, they have specific needs diet wise.
They must be protected against cold, damp, overheating, change of temperature and predators.
And , Bless them, they are the most ill equipped little mammals when it comes to protecting themselves.
They can't turn quickly or kick like rabbits (but my new boar kick 
). They don't dig. They don't really bite (though they have a good set of teeth)
And when they are ill, they hide it very well so you need to be aware what to look for.
I'd possibly leave overnight if they had fresh food, water, hay, pellets, but not longer.
I haven't left our boys unless they were in Small Animal Boarding.
And 2 are best. Either 2 sows/ 2 bonded males or , neutered boar + females (some rescues will neuter to match boars)
that was an essay, but it's alot to think of.
If you decide , mmm, no, then fair do. They aren't for everyone (my NDN has hamsters and thinks GPs are as ugly and boring as sin)
But I', sometimes tempted to phone the people of Gumtree who advertise their Guineas "child lost interest/ I can't give them time/ new dog" and give them a piece of my tiny mind. But I haven't quite reached nutter status. So I stand about in Pets @ Home. When RandomSmallChild says "I want a GuineaPig". And the parent says "I'll get you one"..............
Well, DD and I tell them what they're letting themselves in for. Sometimes they beat a hasty retreat from the pigs.