Being a trustee isn't just for professionals or people 'minding the family assets'. It is common for people from all walks of life to become trustees of local charities, schools and the like. Usually, the trust deed contains a clause which protects the trustees from liability for an accidental or negligent breach of trust. Normally, this will protect a trustee from being sued for losses to the trust as a result of any actions they have taken, except dishonest ones.
It is unlikely that the trustees will be held personally liable if their actions are reasonable, in accordance with the Trust deed and they take professional advice when appropriate and act accordingly.
It is usually sensible for trustees to purchase indemnity insurance – especially where the assets of the charity (or its income) are substantial.
Good sources of guidance for trustees of charities can be found here.