When you are in court for a hearing, the judge or Magistrate will consider Evidence. Evidence is presented through testimony, which just means something a witness under oath talks about in court.
In almost every case you and the other party will be witnesses at any Hearing. Other people who know you, or who know your kids, or who have knowledge of other important evidence that is relevant to your case might also be witnesses. Other witnesses might be: your accountant, your kid's teacher or principal, and your kid's therapist.
TIP: Talk to your lawyer if you have one about the people in your life who know about your family. They might be witnesses. If you don't have a lawyer, you may want to have witnesses come to court with you to talk about the issues in your case.