Quoting snglemama:" my kids are 10, 8, and almost 4. They all get up early. They don't even wake me up anymore. I tell them ... [snip!] ... They do it to be nice, (letting mom get more sleep), but I tell them they should get me up when the youngest wakes up."
We did this to my dad too when we were young. We loved having morning time without dad around lol.
As for the divorce thing--sounds like hes gonna blow anything out of proportion so "sleeping in" isnt gonna make a difference. lol. If anyone were to ask your kids about it, they would say why they do it--to let mom rest. I dont see anything wrong with that at all, and I doubt anyone else would either. It would be a different story if one of them was a baby. I would trust my 3 year old to get up with her older siblings in the morning. *shrugs* I wouldnt worry about it, you're a great mom!