from typing import List
from typing import Tuple


def find_unique(children: List[int]) -> Tuple[int, int]:
    """Find unique item and return difference from other items and index."""
    first, second = set(children)
    if children.count(first) == 1:
        common, unique = second, first
    else:
        common, unique = first, second
    return common - unique, children.index(unique)