John and Mary are married, and have two children by that marriage, Bill and Mike. Before the marriage, John had a child out of wedlock, Sally, but John has never told Mary about Sally. During the marriage, John had another child out of wedlock, Cathy, but John has never told Mary about Cathy either.
When John and Mary set up their estate plan, and when their attorney asked them the names of any children that both of them or either of them had, John did not mention Sally or Cathy. If the attorney prepared a trust or Will that gave everything to ‘the children’ that term would be ambiguous and could cause Sally and Cathy to get part of the assets even though John does not wish this result.
Even if the trust or Will states that Bill and Mike (ie. they are named and not merely referred to as ‘children’) receive everything when both John and Mary have died, there is still a problem. That problem is called pretermission. By failing to have been mentioned by name (ie. by failing to have been specifically disinherited), Sally and Cathy are legally entitled to receive the share of the assets that they would have gotten had John died with no will (this is called the intestate share).
John’s act of concealment endangers the inheritance of the people who he wants to receive his assets after Mary’s death, namely Bill and Mike. His reasons for not telling Mary probably seem valid to him, but John needs to understand that naming all of the children in the estate planning documents and specifically stating that each child inherits something or nothing is critical in order to prevent unmentioned children from inheriting a statutory share.