The General Care and Maintenance of Bearded Dragons by Philippe de Vosjoli and Robert Mailloux
is a very good resource that can be found at many pet stores.
I have a 75 gallon terrarium that I used for my dragon, I think that's big enough for 2, but probably too cramped for 3.
They don't need to be bathed, though wiping down with a damp cloth is a good idea when they get feces dried on them. And their droppings stink something fierce. Seriously, you wouldn't thing something that small could produce such a stench.
You should probably get two, so your kids can see the head-bobbing and arm-waving social behaviors, although they tend to be mellow and most of the time they just sit there. One thing to watch out when you're handling them is that they'll sit still for a long time and then suddenly dart away, even if you're holding them high above the ground. They also have a tendency to run into walls at full speed
but mine never injured herself.
As for the noise level, I don't it will be an issue. Just make sure to train your mammals to stay away from them, and only have them out of their enclosure under close supervision.