If we ignore almost all of human history save for the past 50 years, then yes. If we redefine marriage to not mean what most humans that have ever used the word meant by it, then yes.
But why would we do these things? If you call all relations between two human beings marriage, you gain nothing, you just lose a word.
Marriage is a covenant between two people, a man and a woman, with God, and incidentally, this covenant, not a piece of paper, it's also a precondition for two people to live together and in harmony. It's a commitment by both people to focus not on themselves, but on the family unit and the wellbeing of that family unit.
> You can do so without being married and having children, and it's everyday more common.
Children of married parents still have better outcomes, and the lower income people are, the bigger the advantage of having married parents are.
