I want to do whatever I can to help (but not enable) them to break the terrible money-management example set by their parents and successfully manage their own finances.

Why not set up a fake portfolio? They have X amount of fake money to invest, and they can track those investments. It gives you a chance to teach them. Once they see the positives in investing, they might be encouraged to start saving now. Or, at least talk to them about setting up and following a budget.

On a side note, I started a savings account for my nephew a few months before he was born. I have no intention of ever telling him nor my sister about that account. It is for college, but I don't want either of them relying on it and, hence, not preparing for college expenses themselves.