Our wills are drafted in accordance with current best practice and they incorporate the Society of Trust and Estate Practitioners Standard Terms (2nd Edition). These give the Executors all the powers they need to make sure that the Guardians are not left out of pocket and the children properly provided for.
You do not need to add any extra wording to the wills. In fact if you do so this could lead to confusion or dispute.
If you want to set up more complicated trusts e.g. providing for different terms if your children remain in full time education then you should consult a specialist trusts solicitor. These are difficult to set up and they may have unintended tax or cost implications for your estate.