Grandparents don't have rights under the Family Law Act 1975, only children have rights. Those rights are to know, spend time and communicate with both of their parents and other people relevant to their care on a regular basis, insofar as their best interests can be met. 'Other people relevant to their care' expressly includes grandparents, so if this were to appear before court, it wouldn't be *your* rights that you're asking the court to uphold, it would be *the child's* rights to spend time with you.
However, the fundamentals are correct. You must first attend mediation with the parents to try and reach agreement about when the child spends time with the grandparents. If agreement can't be reached, you will receive a s60i certificate enabling you to file an initiating application for parenting orders through the court.
Hope this helps.