If (b) happens and children survive, guardians and trustees (who may be the same people) need to be appointed to care for the children’s welfare.
Say one of the guardians is required to give up work to care for the children, could they sell assets in the estate to cover for their loss of income (e.g. to pay their mortgage repayments, for example). Could they conceivably “spend” the entire estate in looking after the children and leave nothing for the children at age 18 – this probably goes to the question of whether the same people should be guardians and trustees.