The question is difficult to answer as there is no indication of how much dose was received or when it occurred compared to the births. Also "massive" can mean different things to different people. For example, a dose of 4.5 Sv would be expected to kill half of the exposed population. The current recommendations of the ICRP suggest that genetic effects can occur at the rate of 0.013 per Sv of dose received. Contrast this with the natural occurrence of genetic disorders affecting 7.29 percent of live births. So to determine the likelihood that the disorders were radiation induced more information would be required so that a "probablity of causation" could be evaluated.
Regrettably a genetic disorder does not carry with it the cause, so there's no definitive test to identify why these things happened.
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