Kids need boundaries and discipline, and they're looking to you to get them. Set clear guidelines for your kids (i.e. no snacking before dinner, only one hour of television a day) and make sure you, your partner, grandparents, and any caregivers follow them. Inconsistent patterns and behaviors — no TV when you're home and all-day Disney with Grandma — are a surefire way to spark a tantrum.
Source: Flickr User mdpai75