I am an only child. I've heard that only children tend to have a harder time making friends, but I'm not sure that's true.
I am not any only child because i have one sibling but I have also heard they do have a harder time with friendship. 
From my experience, it encouraged me to actively seek out friendship more, so I became more skilled at conversation and meeting new people.
Throughout history, only children were relatively uncommon but I believe that this is becoming more common now with how expensive racing kids are. 
I agree! There is also a lot of competition to throw elaborate, expensive birthday parties and buy the best things for your child. I think if you are careful it can be more affordable.
In china parents were only allowed to have one child through 2015 because of all of the people living there already.