Philip can tell time(he better be able to he's 9, lol) and has a clock in his room so he can get up after 7am. If he wakes up prior to that he is suppose to either go back to sleep or read quietly in his room. We tell Lindsay that she needs to stay in bed until the sun is up or I come in and tell her it is time to get up.
It took a while but when they get up on weekend mornings they will go and watch tv or play quietly for about half an hour. After that they are up and awake and just can't seem to be quiet. If I remember correctly we started by one of us getting up with them, or a little before them. We would whisper and tell them they needed to be quiet so Mommy or Daddy could sleep longer. We would head into the living room with them and do quiet things. Sometimes we would turn on the tv if one of their favorite shows were on(Dora, Thomas, etc). Sometimes we'd color or read stories. Basically anything that would keep them quiet and entertained. I think this worked for us though because my kids don't want breakfast as soon as they wake up.
The bursting into the room mostly stopped when dh came up with the idea of having them leave the room and try again. He would have them stop, go back out, shutting the door behind them and then knock and wait for us to ask them in. It took a while to get that to work but it was worth it. I'll sometimes hear them running down the hall and then they will pause right outside the door before knocking.
We have finally got our 4.5 year old staying in his room until we go and get him.