Well the separation is not “legal” technically but not all cases necessarily need a “legal” agreement. If it’s been over one year then you can file for divorce.
As for the child support, if you have primary custody (i.e. the child(ren) are living with you)then the best thing to do is contact your local Department of Health and Human Services (DHHS) and set up an appointment. Or you can wait until the judge hears the case and makes his determination. But the DHHS will represent you for free in court as their funds are received from the state in proportion to how much child support they collect (or so I’m told).