How does a children's aid society investigation get shared with the family court judge in a parenting dispute?

There's no automatic pipeline between a society's investigation and a judge hearing your parenting dispute - the two are different proceedings under different statutes, often before different courts, and a society doesn't routinely forward its files to a family court judge on its own initiative. Information generally reaches the judge only if a party puts it there: filing an affidavit that describes the CAS involvement, calling a worker as a witness, or bringing a motion asking the court to order the society to produce its records.

Children's aid societies treat their files as confidential, so simply asserting "the society is involved" is not the same as having admissible evidence about what the investigation found. A parent who wants the investigation's contents considered usually needs a formal production request or subpoena, and the society or the other parent can resist disclosure on privacy or ongoing-investigation grounds. If a unified Family Court branch is hearing both matters, coordination is somewhat easier, but the records still don't transfer automatically. Speak with a lawyer early about whether a formal disclosure motion is worth bringing in your case.