Perfect parent...obviously not....

Where is it in the manual that parents have to like all their children?

I only ask this because I recently had to wake up to the fact that whilst I love all my children equally, and would never change them for the world (despite REALLY not looking forward to when I have three teenagers in the house at the same time as a small person) I actually find one of them more difficult to get on with then the others...

I was somewhat worried about this untill I rationalised it as the same issue you have with all relationships - YOU CANNOT LIKE EVERYONE YOU MEET - even though this particular person is genetically half me, and therefore I am effectively saying that there's something I have "created" which I don't get on with.

Still, even though I have been through this thought process there are pangs of guilt whenever I realise that my child is not necesarily getting the full emotional imput that they should be, from me, and that I sometimes find it really difficult to not get one sided about the challenges they present me with on a daily basis.
So,
I made a concious decision to separate the "dislike" into a place where it does not affect my behaviour towards my child, do everything I can to ensure even-handedness in ALL my responses to their behaviour, including issues between them and their siblings, and to work very hard to show them that I do love them, respect them & completely support them in everything they do.
I would still like someone to help me here though.... I know I'm not a perfect mum but surely I should be able to manage this?