What you can do is attend a family dispute resolution conference with the mother, which is where discussions are mediated by an objective third party to keep them focused on what's important and try and negotiate a parenting plan. Both parties can be represented legally in this process.
A parenting plan is a document that outlines who the children live with and what time they spend with the other parent. If you both agree, you can also have it made into consent orders so that it is legally enforceable.
If you're unable to reach agreement about a parenting plan, however, you will receive a s60i certificate, which will enable you to file for parenting orders through the court.
It's best to avoid court because it's very costly and time consuming, but the children do have a legal right under s60B of the Family Law Act to know, spend time and communicate with both parents on a regular basis, so if the other parent refuses to enable them to enjoy that right, then you may have to go to court for remedy.
The court determines parenting orders based on the children's best interests, and the pathway it uses when deciding is under s60CC of the Family Law Act.
However, if things have been fairly amicable for some time, then hopefully court won't even be necessary.
I hope this helps.