Disadvantage of having only one child

Our class already talked about which number of children is a perfect number for family. Most students said that they want to have two children in their future. I already have two children so I am happy^^. In my case, two children can make harmony very well. The elder usually helps the younger for example, in reading, cleaning, and playing. Also, they rely on each other during their outside lives, without parents, for example in school or camp. Sometimes they argue for each one’s profit, but it is natural, because they can experience small society with competition. I saw the cases of having only child, which seem not good for them. Then I saw a child who is usually selfish and stubborn. I think that having more children is better than an only child.