My brother and SIL put a timer on the lamp in my nephew's room, and told him he can't start talking/making noise until the light goes on.
When we transitioned from crib to toddler bed, I closed my boys' door (we've closed doors since they were babies, so this was not a really huge change for them) and have a child proof door handle lock on the inside of their door, so we avoid wanderers or too early of risers. I also avoid feeding them immediately upon waking, so as to not train their tummies to wake them up, if that makes sense?
They still wake between 7-7:30 AM, after about 11-12 hours of sleep, and they are 4 and 2 1/2.
If we have a super early morning (which thankfully doesn't happen very often!) wake up - maybe between 6-6:30 or so, I will set my cell phone alarm for 7 AM or later, and tell them they have to remain quiet until "the beep-beeps go off". Sometimes it works, sometimes not.
The trick for us is to be consistent, but allow for flexibility within reason. Good luck!