I was looking into that same topic not long ago, and the answer is: not necessarily. You are not legally required to have a lawyer to sort out a child custody agreement. You can file the paperwork yourself, or negotiate with your ex on your own and just have an attorney check your paperwork before you submit it to avoid issues with the court.
That said, there are plenty of situations when looking up “best child custody lawyer near me” is the best course of action. As the Kaspar & Lugay LLP website explains, child custody cases can get complicated, and working with an attorney is your best chance of securing the best possible outcome. So you should definitely contact an attorney if your former partner has already lawyered up, or if they changed their minds about letting you share custody, or if they have suddenly started making false accusations and questioning your ability to be a responsible parent.