In addition. I have a brother who is 10 years younger than me. I am mid 50s and he is mid 40s. It was fab having a little brother to start with as I had been an only child til I was 10. Although I liked being an only child, and was never short of company as I had lots of friends, and also 7 cousins, I was excited to have a little brother. I used to babysit him and play with him, and I taught him to swim and ride a bike, and we had a good time til he was about 8.
Then he (understandably) started playing with children of his own age and made lots of friends, and I was 19-20 by then, and moved out, and away from home (some 15 miles that's all.) And we didn't see each other much, but still remained fairly close.
When I was 35 and he was 25, he met a girl, and moved in with her family, and a year later, he moved to Canada with her and her parents and married her over there. 15-16 years ago now. I was pretty sad, and my parents were devastated. It's his life of course, but their son was just gone, just like that.
He visited once, 2 years later, and we visited him 2 years after. That's it. I haven't seen him for 11-12 years. We keep in touch via facebook, but for various reasons I won't go into, I am not able to travel abroad, so I don't know if I will ever see him again, and I haven't got to see my 3 nephews grow up. He says he can't come here as they can't afford it.
My parents died close together 8-9 years ago, and it was me who had to do everything. He didn't even come to their funerals as he was had work commitments at the time. (BOTH times.) I think he just couldn't be bothered, but he insists he couldn't get away.
So even though I had a brother, I was completely alone in caring for both my parents when they were elderly, (they were sick, and ailing for 3-4 years before they died, and I was run ragged looking after them, as well as working, and looking after my OWN kids.) And I had to deal with the funerals and everything.
So the comments from people on here assuming having a sibling will give your child a lifelong friend, companion, and comrade are laughable.
And don't even get me STARTED on the vile insults aimed at only children. Some people sound so bitter and nasty, that I think they are a person with a sibling (or more than one,) and their sibling(s) have been favoured massively over them.
So it has made them jealous of only children, because of the massive amount of attention and love they have received from their parents. The attention and love they didn't get!