Hi, and welcome to the forum.
I'm glad you're doing your research ahead of time -- a lot of people don't, and sometimes wind up with a pet that's not suited for them.
Guinea pigs are very cute animals, but they're not really suited for small children. They're very skittish, and some of them never really warm up to people, although they are docile after they're caught. Their backs are fairly fragile, so a drop, a fall, or a too-tight hug can harm them. They don't come when called, they don't play with you, and they usually don't cuddle for long. When they do cuddle for more than a few minutes, they'll probably pee and poop on you.
Their cages do need to be cleaned daily, or at least the poop and the peed-on hay needs to be removed. You can go 3-7 days without a full cleaning, depending on what you use for bedding, how big the cage is, and how many pigs you have.
The minimum amount of space recommended for one pig is 7.5 square feet, but that's barely adequate. Every additional pig needs at least another 2.5 square feet. If you have boars, they need even more room.
Unlimited hay is an absolute must -- they have to have a long strand grass hay to keep their back teeth ground down and their GI tracts moving.
To be honest, I wouldn't recommend guinea pigs for a family with kids the age of yours. Our two wanted pigs for quite a while, and I waited until the youngest was seven before I got them. Even then, she needed quite a bit of supervision with them, and still can't catch them herself because she's not tall enough to reach the back of the cage. She got a puppy for Christmas this year, and is much happier with it than she ever was with the guinea pigs.
When all of your kids are in school, you can reconsider guinea pigs. The kids will be old enough to help take care of them, and to hold them responsibly. At the ages of your kids, the one-year-old wouldn't be able to interact with them at all for fear of his accidentally harming one, the three-year-old would require constant supervision with them, and even the five year old couldn't be trusted to handle them properly for quite a while yet.
I'd suggest a cat, if none of you is allergic to it. Cats will play, don't require a lot of care, don't have to be walked in all kinds of weather like dogs do, can get themselves out of the way when they're ready for a nap, and aren't particularly fragile. They will snuggle, which kids love.