The condition the three children were suffering from meant they were unable to talk or walk and were slowly dying.
It has been described as an incredibly debilitating disorder.
The four-year-old girl was diagnosed first followed by the younger twin boys.
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The 24-year-old was unarmed and the incident is not being treated as terror-related.
Some platforms have been taken out of service with disruption expected to continue until the end of the day.
The Met Office has extended its weather warnings for snow and ice to cover vast swathes of the country, including London and the South East.