I dont have children, but my two best friends do, one has 3, one has 1.
The one who has 3, while happy her life is dominated by children, she left her job as was finding juggling too much, she rarely has opportunity for social events, they don't have holidays, sometimes it feels that when you are talking to her that her mind is elsewhere, she can never truly turn off mum mode. I'm not saying that is a bad thing, some women absolutely thrive off that and that's great, but I'd personally see it as a negative.
My friend who has one, finds child care an absolute doddle, apart from when he was a baby I don't feel it changed her social life, she was still up for weekends away with her friends, meals out, nights out etc. She seemed to be relaxed and more comfortable letting loose, she has excess money, despite her and her husband having fairly average jobs she takes her child abroad 3-4 times a year and camping about 4 times a year, her child is absolutely excelling at school, gets plenty of 1 on 1 time at home, has plenty of friends who live local so hasn't missed out on socialising. She doesn't think she'll have a second as she wants to be able to set the child up well for future (savings) and doesn't believe she can do that with more than one.
I am planning to have a baby next year and I can see an awful lot of benefits stopping at 1.