Men and elves are children of Iluvater.
Elves were also known as the children of Eru, and awoke by the mere of
Cuivienen (water of awakening) - These people were called Quendi (elves)
Eru, the one, whom the earthborn knew as Iluvater, created the fairest race
that ever was made and the wisest. Iluvater declared that elves would
have and make more beauty than any earthly creatures and possess the greatest
happiness/deepest sorrow.
Then Men, known as the secondborn, came with the rising of the sun, and Men
first opened their eyes in the land the elves called Hildorien (land of
followers) Elves called the men the Engwar (the sickly) because they were short
lived, weaker and less noble of spirit in comparison. The men that didnt
succumb to Morgoth (those that fled North and West, to the Noldorin - where the
Noldor accepted the allegiance of men and thus men became known as Atani
(secondborn) then Edain (second ones).
*Just thought I'd add a little background - sorry about the length!*
Elvendala