I share a DS with iklboo great manners, generous, kind, sociable, likes being in a group or at home, great with babies/toddlers (he's 8yo), great with his own age group, great with adults. Not precocious, not spoilt, not demanding , he hears the word no plenty!
People come out with some right fucking cobblers about single children.
My sister has resented me since birth, we're now mid-40s, it got boring really fast. DH is 3rd of 6, he now only speaks to one as the others are money-grabbing, spiteful tosspots.
My best friend is one of 9 and they are all delightful and have a great family bond, with all their children, too.
You never know if a sibling is going to be a blessing. We decided to stop at one, lovely pregnancy, shitty birth. I'm not less of a mother because I have one child.