Do you have any brothers or sisters?
A: Do you have any brothers or sisters?
A: 你有兄弟姐妹吗？
B: No, I am the only child. It's quite common in China.
B: 我没有，我是家里唯一的孩子。这在中国是很普遍的。
A: I suppose so. It's such a big population.
A: 我想是这样。中国人口太多了。
B: Yes. How about you? Do you have any brothers or sisters?
B: 是的。你呢？你有兄弟姐妹吗？
A: Yes. I've got two brothers. They are both younger than me. I'm the oldest.
A: 有，我有两个兄弟。他们都比我小。我是老大。
Notes:
1. To ask about someone's family, you can ask: Do you have any brothers or sisters; Do you have any children? 要问某人的家庭情况，你可以问：你有兄弟姐妹吗？/你有孩子吗？
2. If you have no brothers or sisters, you can say: I'm the only child or I'm a single child. 如果你没有兄弟姐妹，你可以说：我是家里唯一的孩子，或者我是独生子。
3. If you do have a brother or a sister, you can say: I've got a sister. 如果你有兄弟或者姐妹，你可以说：I've got a sister (我有一个姐姐/妹妹)