I think we are all big boys and can figure out when is appropriate to watch TV if you are behind the wheel. If someone is daft enough to watch TV while driving behind the wheel they will most likely be on the phone anyway so who's to know which caused the accident they get in.
Worth pointing out that Insurance is invalidated and insurers are checking models with TV systems in the event of an accident claim. Could lead to dangerous driving charge and a prison sentence. Better to get rear screen DVD system as reception won't be that great for kids/passenger anyway.