Is three too young for CBBC?

My husband and I have different views on what constitutes suitable viewing for our son.  I am quite happy for him to turn off In the Night Garden, Teletubbies or Waverloo and choose a programme on CBBC instead. In fact, I probably encourage it - I can't stand those particular programmes - they seem so infantile and so patronising to me... I just looked up the FAQs on In the Night Garden to work out what age range it is aimed at.  I was amazed to find out that there is a whole ideology behind the show, apparently, and it isn't just mindless babble.  Obviously my degree in English Literature has not given me the right tools for analyzing this particular artform.  Will have to work harder if I am going to continue to write this blog!!!  Anyway, enough about ITNG - the fact is that I am happy for my son to choose The Sarah Jane Adventures, for example, instead of ITNG, believing that if he watches it then he must be understanding a certain amount of it and if he understands it, then he will be being stretched and challenged, picking up new ideas and new vocab.  But my hubbie is horrified by this attitude and thinks SJA is far too grown-up for a three year old and will scare him. 
We had a similar conflict over the Harry Potter films.   Knowing my son loves wizards, witches and all things magical I thought he would love the HP films.  I got the first one out of the library and he watched it with me, aged two and a half, but when my husband found out he was horrified and wouldn't let us get any more out - even though my son really wanted to watch more.  A seemingly liberal friend with daughters aged 7 and 5 wouldn't let them watch the films at all, making me feel that maybe I had been a bit rash. 
I took a look at the British Board of Film Classification website and was surprised to see that U is recommended for young children aged over 4, and PG is aimed at children over 8.  On the BBC website I found some recommendations stating the CBBC is aimed at 6 to 12 year olds, and so I guess that means Cbeebies is aimed at 0 - 6.
However, I'm sure all parents would agree that a five year old has very, very different needs to an eighteen month old, and a six year old has very, very different tastes to a twelve year old - so I think that these broad categories cannot be taken too literally.  Rather, I think different programmes will suit different children at different stages in their lives, and if parents or an adult watches the TV with the child they can then answer any questions, explain any mysteries and as a last resort turn the TV off if things become too scary or inappropriate.