It depends on whether you have a parenting plan or formal consent or court orders. A parenting plan isn’t legally enforceable, so a breach doesn’t carry direct legal consequences, though it can still be relevant evidence if matters later go to court.
If you have consent orders or a court order in place, a breach can be addressed through a contravention application. The Court can order a range of responses depending on the severity and pattern of the breach, including makeup time with the children, attendance at a parenting program, fines, or in serious or repeated cases, a variation to the existing parenting arrangement.
A single missed handover due to a genuine emergency is treated very differently to a deliberate, repeated pattern of breaches. If you’re dealing with ongoing non-compliance, document every instance, dates, what was agreed, what actually happened, this becomes important evidence if a contravention application becomes necessary.