what happens if i'm paying child support, and the custodial parent loses custody?

You need to petition the court to terminate the child support payments.  Then it's very possible that her parents will petition for child support. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.