I have seen many couples who had prior marriages and children from prior marriages with the typical mirror wills: everything to my spouse, then to my children. This is a huge mistake. Bob and Jane--second marriage for both--have one child each from their previous marriages. Bob dies and all his assets go to Jane; Jane dies and all her assets (including assets that she inherited from Bob) go to Jane's child. Bob's child has been left out of the picture, possibly unintentionally.
I believe the best estate planning tool here would be a trust for Bob and Jane that would provide for certain distributions to certain beneficiaries at certain times.
For a good article on the topic, see Estate Planning for the Twice Married. (Thank you to Professor Beyer, for posting this on his blog Wills, Trusts & Estates Prof Blog.)