The use of sworn affidavits in a child custody case are allowed, but only in very limited circumstances.
The Kansas Court of Appeals ruled on July 15, 2016, in Lynn v. Lynn (2016) that a Court did not abuse its discretion after making a child custody decision in a Kansas divorce case. At the time of the divorce, the parties agreed to a shared custody arrangement which the Court ordered at the time of the divorce. Not long afterward, the parents decided that shared custody was not working and each asked the Court for residential custody of the children. Mother was ultimately successful, and she was awarded custody of the children. Father appealed, and the appellate Court ruled that the District Court did not abuse its discretion, and had valid reasons for ruling on child custody the way that it did. The Court cited In re Marriage of Rayman (2002), and noted that the paramount consideration of a Court is the welfare and best interest of the child, and that those decisions are entrusted to the sound discretion of the trial Court in a child custody proceeding. The Court of Appeals will not reweigh evidence heard at the trial Court level, or make credibility determinations. Absent an abuse of this wide discretion at the trial Court level, an appellate Court will allow the District Court rulings to stand.
Of interest to some in the written opinion of the Lynn Court is the discussion surrounding the use of sworn affidavits from trial witnesses. This is a question that many clients ask questions about when preparing for trial in a child custody or divorce matter. Often, witnesses try to avoid having to testify in a child custody or other Court proceeding, and as a compromise to the requesting party, the witness will offer to submit a sworn affidavit to the Judge. This is normally inadmissible hearsay and will not be allowed, as the other side will not have a chance to cross-examine the witness from an affidavit. However, the Lynn Court cites State v. Hardy (2015) to explain that if the parties agree that the trial Judge should consider evidence that would otherwise be inadmissible under the rules of evidence (like sworn affidavits), the Judge is free to consider them when making a ruling. My experience is that the best practice is to get a subpoena for your needed witnesses long before your trial, and do your best to secure their appearance at the hearing. As the father found out in the Lynn case which you can read above, affidavits cannot be cross-examined. If you are unhappy with what they say to the Judge, your recourse is zero.