I’m the first of 5, birth years of '54, '55, '56, '61, and '65. I was too young to be much help with all but the youngest. I did my share of diaper changing, feeding, burping, and such. I was also the designated babysitter from about age 12, and luckily, my sibs were mostly easy to deal with - mainly because they knew if they caused trouble, I’d call a neighbor who had full authority to kick ass and take names. 
Not at all. We were kept in separate rooms for good reason. Isolated from nearby cousins too, the pervs.
I was the baby, 3 years younger than my brother. He was not involved in raising me at all. In fact, he was a bully throughout our childhood.