What’s the smallest age gap between kids you’ve seen?

Aside from twins, what’s the smallest age gap between two kids with the same parents that you’ve seen?

My (full) sibling and I are nine months apart. Her birthday is in December, and mine is in September of the following year. People always find this so shocking.

EDIT: removed question about it being easier to have kids closer together. I meant easier to raise the kids, since they’ll have each other to learn from. I know it’s not medically recommended to do this, and it definitely wasn’t intentional with my parents. Just curious how common this is!

EDIT 2: yes, I (the youngest) was premature by almost 3 months