They are lovely pets :)
Your best bet is to get two baby girls (boys can fight and a boy and a girl will have FAR too much fun!!
).
They do need a big indoor cage (as others have said), unless you have somewhere safe to let them run around most days (somewhere that they can't get behind the fridge etc!) and clearly isn't carpeted.
Lots of people will say you can keep them outside all year, but it's really not fair on them - some will live, but many will die.
You need to use hay (not straw or paper) or fleece/towels in their cage. The towels/fleece are great because you don't get the hay traipsed through the house and you don't get the hay smell in the house - but I hated washing them in the same machine as our clothes and doing a rinse between their stuff and ours was a bit environmentally unfriendly and a faff!
There are quite a few things they can't eat - which take you by suprise so you need to check this out carefully.
It is possible to 'toilet train' SOME of them, but it's bloody hard work and not always successful.
If you get them, leave them be for two or three days, just talk to them a bit and feed them - after that you need to handle them a lot for them to become human happy :)
The fleece pouches are really good because their nails are very scratchy. They generally don't bite as such, but don't seem to have good eyesight so tend to nibble on fingers a bit by accident!!
It's great if you can get them from a rescue but we (a friend and I, for her)tried for 6 months, with a radius of 40miles - no luck, so ended up buying from a breeder - we went to her home twice, one by appointment and one 'as we were passing by' she had a lovely set up and offered to have them back anytime if we ever felt unable to keep them for any reason etc and gave us her vets details to check up on her etc.
I personally think your kids are really too small to enjoy them properly as pets and by the time they are old enough the GP's will be older and not so much fun - when they are young they are really playful and jump around, run about a lot... I'd wait if I was you, but if you are buying them for you then go ahead 
I guess you could always start with some older really tame ones - then when they have ..umm... gone to greener pastures and the kids are bigger get some babies?!
I love GP's and miss not having them around - but I'm not in a position to have them right now :(