Children are a natural consequence of marriage in most cases. It's to be expected.

The size of the family varies among our people. At the time we were wed, my husband and I were only children. I never had any brothers or sisters, but not long after our marriage, my father-in-law took a second wife--the only Elf ever to remarry--and produced another four children. It... was not something my husband took well. At times, I think the fact that our union was blessed with seven sons came in part for him trying to fulfill his father's desire to have many children in the household. To my knowledge, no other Elves have ever outnumbered us in this.