First off, let me say that I LOVE ferrets! I had four at one time and each one of them had the most incredible personality. I would buy another one in a heartbeat.
But...I do not think they would be an ideal pet for an 8 yo unless you knew exactly what you were getting into. They are a lot of work. You have to clean out their litterpan constantly (they are only about 80% consistent with using it anyway), give them bathes and clean their ears and clip their toenails frequently to help with the odor. By the time a ferret reaches the pet store, they have already been fixed (you have to have a licence to breed them) and had several of their scent glands removed. But they can't remove them all. And obviously, since the males are much larger, they also create more scent.
Also, they are unbelievably curious little fuzzheads, so you have to meticulously ferret proof your house to keep them safe (the #1 cause of accidental death in ferrets is recliner chairs). They can fit through any hole the size of a quarter.
You also have to be firmly, but gently consistent with their training or they will end up biters. Children need a lot of help to get them past the nipping stage without trauma to either party.
They are also prone to several diseases that can be quite heartbreaking.

Now that I have probably completely turned you off and have the ferret loving population up in arms, let me tell you about the flip side of this coin.
Ferrets can weasel themselves into your heart in nothing flat. They have playful temperments and a problem solving nature that will have you in tears with laughter. I think everyone should experience the Weasel War Dance at least once in their life. And the sight of a 2 pound ferret trying to drag a 10 pound bag of potatoes up a flight of stairs is something I may never recover from.
If you have a cage to keep them safe when you aren't around, or can set aside a room that is completely safe for them, that helps greatly. The baths and grooming aren't hard, especially if you can have someone experienced show you the first time. Keeping on top of things, just like you do with the dog, goes a long way in dealing with any odor. And there are things that you can do to minimize the risk of adrenal disease and the like. The rest of it is worth it. Having more than one isn't really any harder and then they have a buddy to play/sleep with. They sleep about 22 hours a day and then play like mad the other two.
I still had two of my fuzzies when our oldest was born. The ferrets were older by that time and I never had one of them bite her. She is very gently though. Since you don't have toddlers, teaching them how to handle them would be realtively easy.
As pets go, they are pretty inexpensive after the initial shopping spree for supplies. They can't transmit rabbies to humans (but I would still recommend the shot to allay people's paranoia).
Now that I've about written a book..Ferrets are great pets IF you do a little research and know what to expect.
Feel free to ask any other questions that you have.
Stacy

I agree whole hearty. We have had Rats for the past 5 year, 3 different sets. We have made sure to get girls every time. They are very affectionate and sweet and are very forgiving. The ones that my family has had are body rats. They like to climb in my shirt and one of our favorite game is pass the rat (We have the rats run down our arms to the other person.)

My kids were teenagers when we started with rats but they are great pets.

Ferrets make GREAT pets. They don't cause a lot of the allergy problems people get with cats or dogs. They DO however:

Smell if their cage is not properly cleaned. (Kinda Like feet and cheetos...I miss that smell)
Bite like a puppy if not properly trained
take a LOT of TLC and attention
burrow and get into places you would never think they could get to
require a specialy ferret food diet
need shots just like a cat or dog
tend to be EXPENSIVE when it comes to vet bills (They are prone to cancer and tumors, intestinal blockages, and other nasty illnesses)

I would recommend long, hard thought, finding a vet that specializes in exotic pets including ferrets, do your research, and look at how well your home could be ferret proofed BEFORE getting one.

They seem little and cute (which is true, and they always stay that way...playful too) but they are a lot of reponsibility. I speak from experience and my heart...I had two, both were rescues. One died of a ruptured ulcer (We didn't know she had REALLY BAD ulcers, because we weren't seeing a ferret vet for their shots, and she looked and acted VERY healthy). The other died of adrenal disease after two surgeries and a round of steroids....I miss them both so much! But they are not your NORMAL everyday pet and need a little than NORMAL every day care.