There is a good article, written by a vet and published in The Conscious Cat newsletter today,June 2, 2014, about how to best socialize your kittens. It tells you how much handling they need, how many people they should be handled by regularly, and the best age to start. If you follow these guidelines, it will make it easier for your kittens to adapt to a new home with little stress. It's called "Raising Kittens to be Happy and Healthy."
http://consciouscat.net/
http://consciouscat.net/