Sorry to go against the grain but.. YTA.

Your children are being doted upon by their aunt. It seems to me like it's time to do parenting? Sit down and explain that in life, some people are better off than others. Your aunt is better off than you guys are and uses that wealth to be gracious and giving. I say this as someone that was raised in a trailer. Realizing that we were poor was something that became very apparent to me when we visited other homes or on Christmas visits. But my mother sat me down and explained it to me.

You do owe her an apology.

Denying your children access to nice things to acclimate them to having less isn't the way to do it. Tell them that if they work hard, stay in school, and stay on the good path, they can live like their aunt and pay that kindness forward in the same way one day.