The trip to the steam railway was meant to be the highlight of the bank holiday weekend. My son Jamie (then aged 4) shares his father's fascination with steam trains. His lack of interest and pale colour made me realise he wasn't well. That evening, having returned home, it was clear that he was sleepy and did not want to eat his tea; he dramatically vomited the milk I had persuaded him to drink.

His complaint of a headache added to my worry. I did not sleep much that night. …