I obviously can't speak on Applegate and Grant's behalf, but I don't believe any true chaos theory is present WITHIN Animorphs, as in small events making big changes within the story presented in the books, but it does seem implied that the entire narrative has increasingly large ripple effects throughout the universe. To put it simply, the Animorphs, five simple teenagers on an obscure planet of little importance are the butterflies, and from their actions completely changes the course of the Andalites, Yeerks, Hork-Bajir, Taxxons, Leerans, Chee, Howlers, and so on, AKA the hurrican.