1. Your parents have literally no clue what they’re doing when things go awry. Seriously though, since you’re the first, they’re also learning how to be parents for the first time. So sometimes, things go off handbook (like I don’t know, you take a ball of wool and turn the entire house into a giant spiderweb and then crouch on a doorway pretending to be a spider. Not speaking from experience or anything.), your parents don’t really know whether to laugh or to punish you. Sometimes they do one when they are supposed to do the other.
2. You so much as cough as a child, you’re going to the hospital for a checkup. Honestly, if I didn’t want to go to school as a kid (and because I got bullied, I used to hate school with a passion), all I had to do was cough. My mother would immediately panic and keep me home from school and take me to the doctor. My brother never got away with nearly as much faked coughs as me because my parents knew by then exactly when he was making it up to miss school.
3. You’re so much as ten minutes late, they literally send a search party out for you. No jokes. There was once an embarrassing incident in my life where I was at a friend’s party and was ten minutes late getting out. My mother actually sent someone from home to the DJ at the party and made him announce that my parents wanted me home. I nearly died of embarrassment. My sibling never had to deal with any of that growing up. They only worry if he’s more than an hour or so late. As the first child, they will always panic about you and your whereabouts. The second child, they’re used to parenting and have chilled out way more.
4. You get punished a lot more severely for minor infractions. This again, is because your parents are new to the parenting thing with you. So you get the brunt of the bad punishments, the brunt of their anger which could be far worse over something small than it should be. In retrospect it seems like your sibling gets away with lots more than you, but the reason for this is because they have reflected on their own actions and figured it was better to be gentler.
5. You have responsibilities way sooner than your siblings. From helping running the house to discussing financial issues with your parents to babysitting from a young age when your friends parents kids come over to always being made for your siblings and their behaviour from a very early age, you grow up much faster. And if the age gap between you and your siblings is 3+ years, you grow used to being the responsible one and almost like another parent to your siblings.
6. You learn your parents are human and how to appreciate them and respect them despite their flaws. This is an important one. As children you think your parents are all knowing and all seeing and never make mistakes. The truth is, they are human beings and all human beings make mistakes and have flaws. You learn to appreciate your parents good attributes even more when you recognise how hard they are trying despite their flaws and to look after you.