I don't know about the 'cat' case you refer to. I've not heard about it but if, by 'girl', you're referring to a juvenile, it's standard practice that they're not named in court cases. This is to give them the chance to 'mend their ways' without being 'labelled' by the public. (Young people who're labelled as "wrong 'uns" tend to live up to those reputations). Only in very exceptional cases (such as murder) will a judge consider granting permission for the offender's name to be made public.
With regard to the Baby P case, the most likely reason for neither the baby nor her mother being identified is that there are other children in the family. The court seeks to prevent others (particularly the sibling's schoolfriends) from knowing that it was their family involved in the case, in order to prevent bullying or undue pressure on the siblings to tell others exactly what occurred in their home. (i.e. the court is seeking to allow the siblings to have as normal a life as possible, without being constantly reminded of past traumas).
Chris