Sleep question for the moms

In the past couple of weeks, AJ has gone from being our excellent sleeper to being our challenge.  Historically, AJ has always needed a little more sleep than MJ.  From the time they came home from the hospital, he would sleep a little longer at naptime than MJ and wouldn't wake in the mornings after MJ (usually being awakened by MJ, or by us because MJ had been up for a while).

Starting about two weeks ago, AJ has been waking up first. . . and early!  He has gone from sleeping until 6:15-6:45 or so to waking between 5:15-5:30 most mornings.  This change in wake-up time has come without any change in bedtime or change in nap duration, and I'm not quite sure what is causing it.

Now AJ is up before MJ every day, and unlike MJ, AJ is not content to babble contentedly in his crib for a little while when he wakes up before someone comes to get him up.  No, AJ wakes up crying and insisting to be taken out of the crib THIS INSTANT.  This means that someone--OK, *I*--have to get up at 5:15, or whatever ungodly hour he has awakened, and get him up.  And because MJ is a light sleeper, I also have to get him up, too, because invariably AJ's crying wakes MJ up, no matter how quickly I go in to snatch AJ out of his crib.

I'm not sure if this is our "new normal" or a phase or if there is something that can be done to change this pattern.  I know that AJ is probably due to get some more teeth--at 19 months, he still only has four teeth, though several more are visible right under the gums--so maybe teething pain is a factor in these early wakings.  Additionally, he has had a ravenous appetite lately.  The amount he is eating has increased 50-75% from his usual amounts over the past few days; some days, he eats almost as much as I do. . . and that's saying something, considering that he weighs under 23 lbs to my (ahem) 200-ish lbs.

This morning AJ woke at 4:00 a.m. (GAH!), and fortunately I was able to quickly retrieve him from his crib before he woke his brother.  He slept in the guest room bed with me for a little more than an hour more (we generally don't co-sleep, but desperate times call for desperate measures), until he awoke at 5:10 signing and asking for "cracker."  (Dude has a serious graham cracker addiction lately; he eats several a day on top of his usual meals and snacks.)

I tried to put him off by telling him it was too early.  His response was to slide down off the bed and toddle out to the kitchen on his own.  

Fellow moms, any thoughts on what may have caused this change in AJ's sleep habits and what we can do to get him to sleep a little later?  I'd like him to sleep in not only so that I can get a bit more sleep--I'm usually up at 5:30 anyway--but also because he seems pretty tired all morning these days when he gets up this early, so I'm concerned that he isn't getting enough rest.  Plus I feel bad for MJ for getting woken up every morning.

Thanks!