By "small groups of children" I'm assuming you mean those raised by incestuous couples. Same sex couples are proven to be capable parents, incestuous couples are not. I'll support the marriage of couples who have a body of evidence supporting their effectiveness as parents.You have no rationale for why we should help large groups of children but not small groups of children.
Of course I care about children. Demonstrate that there are children being raised by incestuous couples and that those couples are capable of effectively raising children, and I'll support incestuous marriage too.Maybe you just don't care about children.