Wait until your child comes home from a play date of a child with a few siblings - usually it's 'I'm so glad I don't have brothers or sisters!'.
I'm the youngest of many. Basically left to my own devices as a child by parents - too busy with the teens, business, elderly parents and let's face it, the shine goes off when you get to 5... hence only one fuzzy photo of me as a baby - or we think it might be me as it's hard to tell, or it could be grandpa holding a bundle of towels for all we know. Grandpa did treat me well - he loved having a little granddaughter but he died when o was about 3.
Never got to go to clubs, brownies or sports activities because everyone was 'too busy'.
Never anyone to help me with homework (eldest sibling did but emigrated when I was small and the rest weren't remotely interested).
Haven't had more than a dozen conversations with one particular sibling on my whole life - he basically ignored me when I was little (can't say I'm bothered as they are very odd).
Not the 'golden' child or eldest, so never really focussed on. Mum never did know why my first degree was in (I'm not even joking).
I was always teased for being small/youngest and pretty much grew up a doormat. I kept my head down, opinions and tastes to myself (thus avoiding the risk of piss taking) and became very introverted, insecure and shy. Often reminded that I shouldn't have been born as mum was pretty ill and had been warned not to have more children (like that's my fault) and how she had been advised to terminate by her own mother. Grandpa said 'no way!'
Lord, it's all coming out now!
So just because you have siblings it doesn't mean you will get on with/talk/like them. And when your parents become old and/or infirm it's often one child who drops everything to help (funnily enough oven the child who was not the golden or preferred one).
Enjoy your child, focus on the good stuff and not the 'what if's.