Perjury is a felony, usually punishable by up to 5 years in prison. It is easy to say or "prove" that one person's testimony differed from another's, or from the "truth" but it is very hard to prove that the witness lied or perjured him/herself. In order to commit perjury, the witness would have to knowingly, intentionally testify falsely on a material matter. A person accused of perjury can say he mis-recalled, mis-remembered, forgot, misunderstood, etc., all of which are not lies or perjury. In other words, it is easy to call "perjury" hard to prove in court to a jury by a "beyond a reasonable doubt" standard. All Prosecutors will be very reluctant to charge perjury in a family law case, because they could do that all day long and nothing else if they wanted to.
Normally a prosecutor charges crimes that they think they have probable cause to file and exercise their discretion to charge. If perjury takes place in a court room in front of a judge, on the record, the judge would also have the option of initating contempt of court proceedings, or asking the prosecutor to consider taking action. Neither are required to do so, however a person who feels aggreived can make a complaint to the prosecutor.
In addition to the comments of my colleagues, you should understand that to be perjury, the statements must be material, meaning they must have been important facts, with intent to mislead the court, not misstatements or mistakes.
If you think the facts are compelling enough to pursue perjury charges, you can take your complaint to the county attorney, they have the duty to prosecute crimes, not the judge. You might also discuss this with the attorney you worked with on the custody case.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.