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Were Adam, Eve and their children alone?

It depends what you mean by "their children". If by "children" you mean Cain, Abel and Seth then tradition suggests that Adam and Eve had other sons and daughters. For instance, the JPS Torah Commentary explains Cain's reply to God's sentence "whoever will find me will slay me" in Genesis 4:14 as an indication that any future children of Adam and Eve will seek vengeance against Cain.
In Genesis 5:4 we are told that Adam and Eve had many more children without further details. It would seem that the text of Genesis was written with another text as a backdrop for Genesis is terse when it comes to these details and while the details are not relevant to salvation they would be helpful to understand the larger context.
Be it as it may, we are given to understand that Adam and Eve had many more children owing to their longevity and to God's command to fill the earth. How many and who were they we do not know. On the other hand, if the purpose of your question is to find out if there are any human being that is not a descendant from Adam and Eve then this question is either to answer since it is an article of faith that all men and women are children of Adam and Eve.
A quote from paragraph 37 of the Encyclical Humani Generis from Pius XII should suffice: "For the faithful cannot embrace that opinion which maintains that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent of all, or that Adam represents a certain number of first parents." The theological reason behind this principle (known as monogenerism) is of course the universality of Original Sin which every man and woman inherit from Adam and Eve for if there were men who were not born of Adam and Eve, they would not be subject to Original Sin and they could -- on theoretical grounds at least -- be admitted in Heaven without needing to be saved by Jesus Christ. Therefore, the Church affirms that all men and women descend from Adam and Eve.

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