Courts used to use something known as the tender years doctrine when determining child custody. Essentially, it said that young kids were better off with their mothers in these formative years. That's why mothers were more often given custody rights in a divorce.
However, there were a few problems with this doctrine, and most courts now try to find a co-parenting solution so that the children see both parents, not just the mother.
One problem was that research simply showed that kids were typically healthier and happier when both parents were involved. By adhering to the tender years doctrine, courts were making this impossible and children suffered for it, this research claimed.
On top of that, some studies found that children and their fathers often drifted apart. When a father barely saw his kids for years on end, they became less and less a part of his life. This relationship didn't always pick back up when the child got older.
In fact, some have even argued that the entire doctrine was just a way for the courts to violate the fathers' constitutional rights. It was forcing them to be less involved with their kids, even in cases in which abuse and other issues didn't exist. These fathers had done nothing wrong, but they weren't being given a fair amount of time with the kids.
As a parent, it's critical that you know your rights, know what the goals of a modern divorce court are and know what legal options you have. Parents who are very active in the process may be able to work toward an agreement that is fair and that benefits everyone involved -- including the children.
Source: Psychology Today, "Helping Children Survive Divorce: Is Co-Parenting A Good Idea?," Joseph Nowinski, accessed Jan. 26, 2017