If your ex's parents are about to declare bankruptcy then that $600 bill will probably never get paid, or will only have a fraction of it paid. They quite possibly refused your money knowing this. The merchandisers will still get paid, so it's the credit card company that will lose out.
Once they are bankrupt, their generosity with the credit card company's money will probably stop in any case until they have built up their credit enough to start the cycle again.
The only thing you can do is try to ensure that your daughter grows up with a healthy attitude to money and finance. In other words, that she takes her cues for you rather than from her father and his parents.