For those who remarry late in life, bypass trusts may be helpful to ensure children aren't cut out of inheritance if their parent of the new marriage is the first to pass away. Liz Weston has a useful article explaining how bypass trusts work in the Q&A section of her website:
Instead of allowing each other to inherit everything outright, you might want to consider a bypass trust. These trusts allow the surviving spouse to benefit from the assets during his or her lifetime. Upon the surviving spouse’s death, the assets are bequeathed to the ultimate beneficiaries.