Factory owner Paul Kenyon, 62, had planned to fly his family to Florida, US, for a holiday to his villa in Orlando, but made the mistake on the Electronic System for Travel Authorisation (ESTA) form his grandson Harvey Kenyon-Cairn needed to get into the country.
Rather than ticking no when asked "Do you seek to engage in or have you ever engaged in terrorist activities, espionage, sabotage, or genocide?," Kenyon ticked yes, The Telegraph reported.
Harvey Kenyon-Cairns's application was refused and he was asked to attend a grilling from US officials in London.
Kenyon travelled down with his daughter and Harvey's mother, Faye, from his home in Poynton, Cheshirein England to the embassy just three days before their flight, but the visa failed to arrive in time.
He admitted the whole affair cost him an extra 3,000 pounds as he had to pay for extra flights so that Faye, 27, her partner John Cairns, 31, and Harvey could still come with them.
"I had filled in the first five forms all correctly, but it was taking some time. I had no idea I had made a mistake on the baby's form until Harvey's travel was refused to the US. I couldn't believe that they couldn't see it was a genuine mistake and that a three-month-old baby would be no harm to anyone. Harvey was even summoned down for an interview to the US Embassy. I really couldn't believe it," Kenyon said.
"I went down with him and his mum and took him in for the interview, but he can't even speak as he's so young. Americans will be marching against Donald Trump again this weekend," he said.
All eligible international travellers who wish to go to the United States under the Visa Waiver programme must apply for authorisation under the ESTA.