What is the possessive pronoun in this sentence: the idea for a group skate was theirs

Everyone knows that a home should be "child-proof" to protect young babies and toddlers from illness and injury. pets are also in danger from many common household sources which many people don't realize. pets can chew and swallow seemingly safe things, resulting in disaster. it may seem perfectly harmless to toss a pet a grape or a raisin as a treat, but these can be very deadly. although the exact cause is not known, gastrointestinal problems result after a pet ingests grapes or raisins. kidney failure frequently occurs.small amounts of xylitol, an artificial sweetener used in sugar-free candy, chewing gum, cookies, and other baked goods, can cause low blood sugar and liver damage in dogs. all pet owners should educate themselves about these items and the effects that they have on pets. every effort should be made to "pet-proof" homes to provide safe and healthy environments for pets. what is the author's purpose in writing this article?