I'm one of 3, hated it.
DH is one of 3, felt ignored.
DD is an only is really happy.
DH's mother is in a home with dementia, no one visits her. Her 2 daughters live to far way and DH does not feel he owns her anything.
My mother is housebound, no one visits her, I don't because of how she favoured my brother when were kids ( long back story) and he doesn't because he's moved to far way. Other brother out of the picture.
So having any amount of children will not make things easier when it comes to looking after elderly parents.
I see lots of parents trying to juggle time, money and commitments between kids. One 3 year olds spends 4 evenings a week sitting waiting for her elder sibling doing clubs.
My DD goes to PGL every year, many people tell me they'd love to send theirs but, can't afford it of, 2, 3 or 4 of them, little ones would be upset if big ones went without them etc.
Look at the posts about leaving older kids alone, most parents say they could trust the kids, but not together.