I do find the ‘one of each is ideal’ a weird things but.
I know many women in my mums generation who had more kids than they planned to have a child of a different sex. My aunt had 4, in pursuit to get a girl and openly admits she would have stopped at 2 if her second had been a girl and would have had a 5th if the 4th had been a boy.
My dads sister was openly nasty to my parents for getting one of each. She had 3 girls. Mum and Dad just had me and my brother. 4 years apart. We are and always have been close.
I had dd first then 6 years later got pregnant again, I was having a boy. Honestly, I didn’t care either way. I saw advantages to both. A woman at work, was openly hostile to me when I told my colleagues that I was having a boy. Constant ‘it could be wrong it could be a girl’ with a look of distain on her face. I picked a name and it was ‘so what happens when it’s born a girl’ and wasn’t happy with my response of ‘well that name has a well known female version so it will be that’ . It got to the point that someone else told her to shut up.
So I do believe that ‘one of each’ seems to be some peoples ideal.
I do think it’s weird to think that will be close based on sex though. I know loads of people with mixed sex kids and same sex kids. The sex of the kids doesn’t show a pattern.
My Sister in law has 2 girls, 2 years apart who have never got on since the youngest was about 2. My brother has a big and a girl that are 15 month part that really don’t get on. My kids are one of each almost 7 years apart and are super close. Dd just moved away to Uni, ds misses her more than I do. She is contact with him more. She comes home to see him, takes him out for the day and treats him to lunch. She messages him at least once a day to see how school was or how his weekend has been. Her closest friends include him in things they are all doing, where they can.
That’s how me and dbro grew up. His friends became mine and Vice versa. When mum died last year, all dbros long term friends and their partners. got in touch with me personally. Came to see me not just dbro. They are all men. So I don’t find ‘well they are more likely to friends with the same sex so won’t be in the same groups’ doesn’t work either. Dbro married one of my friends.
Dbro is 4 years older than me and his friends grew up with us both. One knew dbro before I was born so known me my whole life. The rest have known me since I was 7. They were at our house a lot when we were young so I think that influenced it.
My dp is the only boy in a family of 5. He is the only one that speaks to all his 4 sisters. All the sisters don’t speak to at least one of the other sisters and it’s always been like that.
Its personality. Upbringing can influence it as well. So I don’t think one of each is ideal, I don’t think multiples of the same sex gives a chance of a better relationship, on its own, either.