Before getting guineas you should go see and HEAR some in person. I find them interesting and amusing to watch, but the noise they make takes a lot to get used to. It still sometimes gets annoying to me.
And, as with all animals in proximity with small children, closely monitor your children around your guineas. Some are more agreeable than others. My 5-year-old boy once got attacked by my 6-month-old guinea cock. My boy was just playing in his sandbox and the bird came over to him and pecked him repeatedly in the face.