I'm in Property Law so I am not sure how much help I am going to be here, seeing as this is more of a Family Law matter. As far as I know, your parents need to establish that they have had some sort of significant relationship with your child, before they will even get near a Magistrate. Seeing as the child is only 6 months old, that's not possible.
These days, especially with Family Law matters most people go through an FDR before they decide to go to court. Family Dispute Resolution. This is when two sides sit down individually with a Mediator to air their problems, then if the Mediator thinks that the two parties can come to some kind of resolution they will organize a Joint Family Dispute Resolution Session.
I guess your parents COULD take this option if they wanted to gain access, but hopefully you could come to some agreement before this matter heads to court, BUT seeing as your parents have no idea about the child even being born there really is nothing to worry about.
BTW don't spend any more money getting legal advice for this matter, there is no threat to your child being taken from you, nor is there any immediate danger of your parents finding out you even have a child, so don't stress too much on this issue, just enjoy your young family. A friend of mine who works in Family Law, her Firm charges $600 per hour for a Solicitor, plus $200 per hour for Administration Duties. Just ring Legal Aid or a Woman's Legal Help Line next time if you need advice, okay?