At present, very little radioactivity can still be detected from weapons tests in the 1950s and 1960s in the environment. If you are warned of an impending attack, immediately enter the nearest building and move away from the windows. This will help provide protection against explosion, heat, and detonation radiation. The 1963 Limited Nuclear-Test-Ban Treaty ended atmospheric testing for the United States, Great Britain and the Soviet Union, but two major non-signatories, France and China, continued nuclear testing at a rate of approximately 5 megatons per year.
A nuclear electromagnetic pulse (PEM) is the time-varying electromagnetic radiation that results from a nuclear explosion. Based on these estimates, the consequences of the more than 500 megatons of nuclear tests until 1970 will produce between 2 and 25 cases of genetic diseases per million live births in the next generation. The highest levels of outdoor rain radiation occur immediately after the arrival of rain and then decrease over time. Since large doses of radiation of approximately 20 roentgen or more (see radioactivity note) are needed to produce developmental defects, these effects would likely be limited to areas of heavy local rainfall in nuclear warring nations and would not become a global problem.
That is, until one of them Googled the safety nuclear bomb how to shelter from the beach and found a Business Insider article titled If a nuclear bomb explodes, this is the most important thing you can do to survive.