This is a frequently asked question in our household these days, & it all stems from possibly the best thirty dollars I've ever spent.
A couple of months ago, Jake & Mallory suddenly began waking up much earlier than they had been previously. They also shrunk their afternoon nap down from a solid 2-3 hours to an hour, tops. I know that I've been blessed with awesome sleepers & that not everyone is so fortunate, but their extreme crankiness led me to believe that they did, in fact, need those hours they were missing. When they showed up in our bedroom at 5:55 one Saturday morning, we'd had enough.
Enter the Onaroo OK to Wake alarm clock, aka "my little lifesaver!"It glows green whenever it's okay for the kids to get out of bed, either in the morning or after nap time. We have it set to 7:00 for mornings & use a two-hour timer on it for naps. Our explanation to the twins was that it was okay for them to be awake early, as long as they stayed quietly in their beds until the green light came on.
We've had our rough days, but this has drastically improved the amount of sleep they're getting & cut down on all of those early ventures out of bed. I think it just helps for them to have some tangible reason for staying in bed, other than just the fact that Mommy said so. Luckily, they're three-year-old brains haven't yet grappled with the idea that the green light's authority is ultimately determined by the time Mommy sets for it to light up!