Early to Bed, Early to Rise

The old saying Early to bed, early to rise makes a man healthy, wealthy and wise...well, in this case it makes a mom annoyed, irritable and cranky! The last two days the boys have woken up at 4:40am-let me repeat, 4:40 in the morning. This is not the first time. Last week they did the same. I was like most of you I'm sure sound asleep when I hear voices that can only be connected to my children. I looked at the clock and think what is going on? I head downstairs and all three of them are wrapped up in blankets laying on the floor or couches watching tv-cartoon network. I tell them it's way too early to be up and they need to get back in their beds. I head back to the comfort of my bed and as I lay there in an unbelievable state I hear voices again and begin to decipher in my early morning brain that they are playing in their room. What the heck?!? I asked Kade the next morning-more like two hours later when it was actually time to wake up-if he woke up because he was cold/hot. He said no, he just woke up. Okay, so if my boys are going to make a habit of waking up before 5 I don't even want to think about what time they will be waking up come daylight savings time. I have no idea what to do...how do you force someone to fall back asleep-you can't, so I have come to the conclusion if they wake up that early I'm just going to let them be and if they are cranky and ornery then they will just have to figure out that they need to stay in bed and sleep till I wake them for school. What else can I do?