The law will make platforms including TikTok, Facebook, Snapchat, Reddit, X and Instagram liable for fines of up to 50 million Australian dollars ($33 million) for systemic failures to prevent children younger than 16 from holding accounts.
The Senate passed the bill on Thursday 34 votes to 19. The House of Representatives on Wednesday overwhelmingly approved the legislation by 102 votes to 13.
The House on Friday endorsed opposition amendments made in the Senate, making the bill law.
Prime Minister Anthony Albanese said the law supported parents concerned by online harms to their children.
"Platforms now have a social responsibility to ensure the safety of our kids is a priority for them," Albanese told reporters.
