If you decided to have only one child then it is important for you to make the child bright and cheerful single child.
1) Dont make the child pitty on him as he has no siblings.
You the person make it clear that it is a private decision made by our family
and put up the "stay out" sign to the busybodies of the world.
2) It is obvious that single children are often very very close to their parents.
Please make sure that your child doesn't become too dependent on you.
Let the child make his/her own mistake and learn from that.