When parents move to a new state, are their wills and trusts valid in the new state?

A will or trust valid in one state is, broadly speaking, valid in all. But there is a big difference in laws that control how married couples own property. In community property states, they share most property, but are free to leave their own half by will or trust. In states that follow the common law system, the name on the title of the property generally controls, but each spouse usually has a legal right to claim at least some portion of the other spouse's property at death.

So you have hit upon one of the few areas in which problems or complications can arise: when a married couple makes these documents in a common law state (Illinois) and then moves to a community property state (Texas).

Complications can sometimes arise in these situations because the property each spouse owns, and so is free to give away by will, may be different in these two states.

In reality, these technical ownership rules probably won't matter much if your mom and dad plan to leave all or most of their property to one another, or if they both heartily approve of the way the property is left. But it is still a good idea in their situation to have the documents reviewed.