An only child has a special bond with their parents, especially since they are the only kid who gets attention at home. When you break the news that you are divorcing, they might immediately feel an anguish since they know it means that they won't see both parents daily. Not having siblings to help them through this time can be a challenge for them. Fortunately, kids are resilient, which can be beneficial for an only child.
If possible, both parents should try to keep a schedule that closely resembles the one the child is accustomed to. This can help younger children to see that there are changes but that most things they are familiar with will remain the same.
School age children might be worried about where they will go to school. As an only child, they count on their friends to be there for them. Try to keep them at the same school if you can so that they can still have that stability and can remain with the same friends and trusted adults.
Talk to the child together. This helps them to know that even though they will have to split their time between both homes, their parents still love them. You might also find that this sets a good foundation for a parenting relationship because it shows the child that they can't try to pit their parents against each other when one does something the kid doesn't like.
Be sure that you have specific points in the parenting plan to ensure that your child can thrive. This might be having a communication policy to help encourage a relationship with the parent who isn't there at the time or even with extended family members like grandparents, aunts, uncles or cousins. Focusing on your child's needs now must be your priority.