The average litter size for beaver is two to four kits.These kits will stay with the family unit for about two to three years until they become sexually mature,then the adult beaver will drive them out of their(the adults)territory.(Natures way of stopping inbreeding)These beaver then have to go out and establish their own territory.Beaver are extreamly territoral and will vigoriously defend their chosen areas.Depending on the available food supply, this factor determines the size of a given territory.