Should Children have televisions in their rooms?

I have five kids. My eldest two daughters, aged 14 and 13 share a room and they have a television in their room. My son is ten and he has a television in his room and my youngest daughters who are 7 and 5 have a television in their room too. However, they only work on D.V.D players, no ariel. What do you think? Should children have televisions in their bedrooms? My teenage daughters are trusted to turn the tv off and go to sleep when they are tired. I make my son turn his tv off at nine thirty, lights out at ten and the younguns, tv off at 8 lights out at nine. what do you think?