When the children were small, we were desperately short of money as my husband became unable to work due to MS. So, all my children learnt very early on, NEVER to try to buy something until they had the money for it.
Has worked well, the only debts any of my children have ever got into are for Mortgage and, of course, Student debts. I so resented this latter, having brought them up with this 'no debt' mantra, I found it dreadfully difficult that the Government was telling them the exact opposite.
The five that went through Uni (at the normal age), ALL worked at evening and weekend jobs the whole time, to help towards living costs. The sixth one did her degree course much later, part-time whilst working the other days, and had the whole course paid for by her employers, the NHS. - so no debt whatsoever. Her only debt, ever, has been her mortgage.
My g.children have all been brought up with the same rules. Those that have chosen the Uni path, of course, are having to take on Uni debts. However, it is noticeable, that they seem to manage their finances, there, much better than most of their fellow students who seem unable to work out how to budget.
It is interesting to note that the daughter who came back to me in such a bad state, (this is the one who eventually did her professional qualification and degree much later), saved all the family allowance for her daughter the whole time, no matter how hard up she was in the earlier years. There is a goodly sum there now, but my daughter keeps it in her own name and no way will let her daughter be able to touch that money until she is about 25 years of age. Will probably be used, eventually, as a deposit for a flat/house.
Good financial management does need to be taught right from the very earliest years.