Among elves, they are seen as outcasts that have purloined the elven lineage. Among humans they are often viewed with suspicion. But I suspect this uneasiness would be displayed upon a full blooded elf as well. Of note is the draw of attention a person of elven heritage exacts from the opposite sex. As mentioned, lifespans of mixed children varies from their apparent age.
Elves live for centuries.
Humans for decades. The mixing of traits affords the child some of the benefits of its elven parent. Lifespans usually exceed that of a human. Most of the time, lifespans reach one hundred to one hundred fifty years. The chance of magical ability is equally present in these people no matter if the mother was elven or human.