Genesis 4:25

And Adam knew his wife again; and she bare a son, and called his name Seth: For God, said she, hath appointed me another seed instead of Abel, whom Cain slew.

1. Adam and Eve had another son named Seth.
2. Eve is quoted as saying that God gave her another son to replace Abel.
3. Either Adam and Eve had very few sons, or they just aren't mentioned (like the daughters they obviously had who are specifically mentioned by name).