Exactly, Spartacus.
This is a 'trans only' event (yet appropriates 'intersex' as a subset of trans, when DSD advocates have indeed been asking for quite some time that trans activists not do so).
This means that 'non-trans' parents aren't able to attend.
Public swimming pools are indeed all ages, WITH PARENTS OR GUARDIANS PRESENT. That is vastly different from a private, no-parent all-ages session.
The information clearly states they privately book the pool and changing rooms. Again, no parental presence for any kids, and no single-sex provision.
DSD-friendly swim sessions, either for adults, or for kids but with standard parental supervision (whether or not parent has DSD) would be wonderful, if not already a thing. That is not what this is.
This thread has been useful to highlight ignorance around safeguarding, and how as soon as 'trans' is added to something, it is treated as not being subject to the same safeguarding standards as anything else. Which is, of course, the basic premise of queer theory - that boundaries should be weakened or dismantled.