Clearly the answer here is send them links to MMM, ERE, MadFIentist, /r/personalfinance, /r/financialindependence, /r/frugal, Bogleheads forums, etc.
Because buying them things to teach them about fiscal responsibility is telling them to act one way when you could be leading by example.
Here is irony- I bought a finance book " rich by 30" for my DD at the thrift store. Two weeks ago.
It was bought new then gifted to someone with a nice 'good luck' inscription. And never opened! Donated in uncreased condition.
So the thrift advice was to buy something new, that is never used, clutters your house and is eventually donated.
Of course DD refused to read it, and so I did, and the advice is good but writing poorly done. Written by a 23 yr old.
Better would have been to take her to thrift store or grocery, give $20 and instruction to buy and make dinner with that.
And then, Get a small " real gift". Don't throw your money away.