The High Court has given a group opposed to plans to make relationship and sexuality education (RSE) compulsory the right to challenge it in the courts.
The Welsh government is making the changes in its new curriculum.
Public Child Protection Wales say parents will be "disenfranchised" from their right to remove children from sex education classes.
The Welsh government said pupils will learn topics that are age appropriate.
Wales' new curriculum is set to be launched in primary schools in September this year, and in secondary schools in 2023.
As part of the plans parents will be unable to remove children from RSE classes.
