My son is 10 months old and occasionally decides that he wants to be up at 5 AM too. He also goes to bed around 7-7:30. What I've found is that if he gets up at 5, he's not actually really ready to be up - is cranky after the first 30-40 minutes up. If I can get him to go back to sleep at 5 (usually after breastfeeding) then he usually sleeps until 6:30 or even as late as 7:15 before waking up "for real". ...which all tells me he's not really ready to be up.
How early are your kids' first nap? Is it earlier than about 9:00 AM? If it is (and I suspect it is), I would try pushing their first nap LATER (maybe by 15 minutes per day) and letting them fuss for a little longer around 5 AM each day. I think what is happening is that their last sleep cycle has become detached from their main nighttime sleep. If you do this then within about a week or so you should be able to get them to "stick" their early morning nap onto their nighttime sleep, thus they will wake up a little later. Then they can go down for a morning nap a little later too. And everything will be great. The Ferber book describes this in better detail than I have here. I did this with my son and it worked like a charm.