A number of suspected child abuse cases in Kerry were not forwarded to the gardaí for investigation until very recently.
Tusla says the delay is "extremely serious" and "completely unacceptable".
It has now alerted the gardaí which is investigating the historical and recent allegations.
Suzanne Connolly, chief executive of Barnardos, says Tusla's mistake is very concerning.
"It is really crucial if we want to protect children who are being abused and ensure that there is an appropriate response that Tusla does make regular and very prompt referrals in terms of concern about cases of sexual abuse to the gardaí," said Ms Connolly.
"In the absence of an effective relationship between Tusla and the gardaí locally, children can remain in really unsafe situations without appropriate support."