Hi,
I'm trying to find some information for you.
Regarding smallpox. The first link in a simple Google search (using keywords 'british smallpox "north america"') reveals a website with some startling information quoted from a book by a reputable publisher:
... Captain Simeon Ecuyer had bought time by sending smallpox-infected blankets and handkerchiefs to the Indians surrounding the fort -- an early example of biological warfare -- which started an epidemic among them. Amherst himself had encouraged this tactic in a letter to Ecuyer. [p. 108]
From: Carl Waldman's "Atlas of the North American Indian" [NY: Facts on File, 1985]
Link: Amherst and Smallpox
There are some other references and information here as well. Try the Google search yourself -- there are some other interesting pages to look at -- and see if this helps you. It seems to be an established and uncontroversial fact that the British used smallpox as a weapon against the natives.
About kidnapping. Google is no real help here. My guess is that kidnapping of native children surely happened, but to find an instance of it, or evidence of a systematic campaign, you will have to do some in depth research. It is well known that early European colonizers kidnapped natives to bring back to Europe (as trophies or slaves), but a systematic campaign to kidnap children is not readily in evidence.
Read this paragraph:
Native distrust of Europeans was not always the result of being pushed out of traditional subsistence areas; some native hostility was in direct response to the common European practice of abducting "exotic" peoples as trophies to provide evidence of new discoveries. These kidnappings soured relations and placed entire regions on guard against future intrusions. For example, in 1502, three Indians fully dressed in native attire were presented by Sebastian Cabot to the court of Henry VII of England. During his reconnaissance of the eastern seaboard in 1524, Giovanni Verrazano kidnapped a small boy and tried unsuccessfully to abduct a young woman. The pattern of selective and random kidnapping continued throughout the sixteenth century. Only a handful of the hundreds (if not thousands) of Indians taken to Europe from the late fifteenth through the sixteenth century returned to their people.
From: "Native Peoples and Early European Contacts." Encyclopedia of American Social History. 3 vols. Charles Scribner's Sons, 1993. Reproduced in History Resource Center. Farmington Hills, MI: Gale Group.
I did a WorldCat search for materials. You might find some kind of reference in this book:
Kidnapped: child abduction in America / Paula S Fass 1997 New York : Oxford University Press, ; ISBN: 0195117093
Otherwise, I suggest looking in thick histories of British colonization for your answer. Perhaps another RR volunteer can recommend one. I recommend submitting another question to the RR site for this.
Does this help?