A normal discretionary trust is just that, a discretionary trust. Your children and yourselves can be beneficiaries and thus receive the profits from the trust and put it towards someone's education. Note that the trusts profits would be taxable.
Take a look at an 'educational bond'. I know a group called 'Lifeplan' provides these. My basic understanding is that you invest through them and the profits are not taxed if used for education purposes. There's lots of other potential tax benefits too. Most of the investments on offer are via the various large fund managers such as Colonial, AMP, etc. Pretty much the same way as super is invested.
You'd need to get specific advice on this. Don't take my word for it, I'm just trying to give you somewhere to look.