As LifeInAHamsterWheel said, BelongTo is problematic, OrionNebula.
It probably started out life as a genuine support group for young lesbians and gays at a time when it was really needed.
But like so many L&G groups, it has morphed into a trans group, the 'T' in LGBT has taken over.
I advise you to look at their website, especially
Coming-Out-As-Trans-BeLonG-To-Youth-Services-1.pdf
which includes references to breast-binding and 'tucking' which are completely at odds with the promotion of body positivity in young people. This is just one example - there are lots of questionable ideas and terminology.
Coming out as Lesbian or Gay doesn't even get its own section - it's all about coming out as LBGTQ+. And they define L or G as being attracted to the same gender, whereas it should be sex. This isn't a technicality, gay people are attracted to people of their own sex, not people of the opposite sex who 'identify as' a man, or a woman.
Coming-Out-YP-2023-SCREEN.pdf
They provide no specific support to young lesbians, their cringingly-named 'Ladybirds' group is open to 'gals' and their 'non-binary pals'. In other words, anybody at all.
Like TENI [Transgender Equality Network Ireland] BelongTo has achieved an incredible level of power and influence in public life, they are regarded as some sort of expert group called into give advice and guidance, for instance to your daughter's school. Why should they? They are not neutral or objective. They are based on a belief system, not on scientific fact.
I'm sure an Educate Together school would not welcome 'experts' from a religious belief system running a Wellbeing project for their pupils, or if they did, they would be sure to have a balancing group presenting a non-religious or non-sectarian viewpoint to the students.
Finally [sorry to go on and on...!] if you and other parents question/object to BelongTo taking this role in your daughter's school, brace yourselves for being accused of being right-wing transphobic bigots.
Unfortunately, there are right-wing bigots who disagree with trans ideology, but for different reasons.
I hope you don't mind me suggesting that if you decide to tackle the school about BelongTo, try not to rise to the accusations of being anti-trans, just keep pointing out that it has nothing to do with right-wing politics or transphobia, it's to do with maintaining standards of objectivity and fact in your children's education.