Surprisingly, custody isn't litigated as much as it could be.
Most parents have an idea of what is best for their children when they split up.
Although the mother is usually the one who has the most responsibility for the kids, more and more fathers are accepting the roll of primary care taker. It doesn't matter who the children live with, as long as the parties do everything they can to keep each other involved in their lives. Unless there is constant abuse and discord, children generally want their parents to stay together. Even when their home life isn't the best, they have a hard time adjusting to the absence of one of their parents. This isn't to say you should stay married for the sake of the children.