Generally speaking, there is a constitutional right to an attorney in a case concerning custody of children, only when the state seeks to terminate a parent's parental rights entirely. But, Colorado goes further. It provides a somewhat more limited right to an attorney, even when parental rights are not terminated, when the state seeks to give a non-parent custody of the child because of a parent's abuse or neglect.
Contested custody determinations are probably the greatest source of unrepresented people in the courts who really need attorneys, can't afford them, and have an interest of sufficient magnitude at stake to justify the expense. Perhaps, in a more enlightened age, the right to an attorney if you are indigent will exist in all cases criminal or not, where someone's personal status, as opposed to mere money or property are at stake. We already do this in criminal cases, civil commitment for mental health cases, and termination of parental rights cases. Extending this to custody cases involving indigent parties wouldn't be a huge leap.