Meta is expanding Teen Accounts - what it considers its age-appropriate experience for under 18s - to Facebook and Messenger.

The system involves putting younger teens on the platforms into more restricted settings by default, with parental permission required in order to live stream or turn off image protections for messages.

It was first introduced last September on Instagram, which Meta says "fundamentally changed the experience for teens" on the platform.

But campaigners say it's unclear what difference Teen Accounts has actually made.

In coming months, younger teens will also need parental consent to go live on Instagram or turn off nudity protection - which blurs suspected nude images in direct messages.

Concerns over children and teenagers receiving unwanted nude or sexual images, or feeling pressured to share them in potential sextortion scams, has prompted calls for Meta to take tougher action.

• Instagram defends new teen safety features after criticism

Prof Sonia Livingstone, director of the Digital Futures for Children centre, said Meta's expansion of Teen Accounts may be a welcome move amid "a growing desire from parents and children for age-appropriate social media".

But she said questions remained over the company's overall protections for young people from online harms, "as well as from its own data-driven and highly commercialised practices".

"Meta must be accountable for its effects on young people whether or not they use a teen account," she added.