Pros have a large family:
Mutual support among family members. Such as older siblings help the other in homework, children help their parents in the home jurisdictions. You can share household responsibilities among family members.
In difficult circumstances siblings can often help each other, or parents.
The larger group is always more fun:) All holidays spent in the large group are wonderful. Another plus is that you always have to speak to someone, you're not alone, you can seek advice older siblings. You can take one example.
Disadvantages are less sure:
Must be shared and often relinquish.
You understand that parents also must share a lot of things between their children.
You have to be tolerant and learn to calm.
I think this is enough:) I am an only child herself, and the sad truth is no sibling ...