DH and I generally refer to each other as Mum and Dad when we are talking to the DCs, as in go and ask Dad something, so I suppose we have steered it a bit. I switched to calling my own parents Mum and Dad by the time I was 8 or 9 I think because it seemed babyish, have always assumed that mine would be about the same. A friend of mine still in her 40's still addresses her mother as Mummy, she says she will never want her DCs to say Mum and Dad, so each to their own I suppose, I guess families tend to follow patterns.