this is a thorny situation. if you made a gift to them, at that time you should have filed a gift tax return. so was it intended to be a gift or a loan? there could be an issue because "gifts" aren't repaid. if they pay you back in a lump sum they should file a gift tax return.
if the IRS were to examine what took place they might argue that what you really did was make an interest free gift loan (IRC SEC 7872) to your parents which under the tax rules would have required you to report imputed interest each year.
