The Department of Internal Affairs says it is having to process up to 20 applications a day for parents who have left it more than two years to register their child's birth.
Deputy-Registrar general of births, deaths and marriages Ross McPherson says the department should be notified within two months of a baby being born.
About 64,000 births are processed by the department every year, and many parents need several reminders of their responsibility, he says.
People who fail to register the birth of their child can be fined up to $1000.