Hello there, may I help you? You are absolutely correctly that watching too much television is harmful to children. They need to be active, outside getting fresh air and being stimulated. There is nothing wrong with an hours down time at a sutiable point during the day watching television but this is terribly worrying.
Here is an article I have found about the psychological damage too much television can do.
As for watching inappropriate violent programs this will only cause a sensitve child to be more upset and disturbed by what they have seen. Your husband is not taking his responsibility seriously and is using television to make his life easier and keep the children occupied with no effort on hos part.