A married couple from Seattle who tried to bring chocolate Kinder eggs home from Canada say they got a much bigger surprise than they’d hoped for.

Christopher Sweeney and Brandon Loo say friends told them about the hollow candies, which contain small, plastic children’s toys, and they decided to bring some home during a recent trip to Vancouver.

What they didn’t know is that Kinder Surprise eggs are illegal in the United States. A border guard pulled them aside while they were headed home and discovered the chocolate contraband in their trunk.

“He said, ‘Are you aware Kinder eggs are illegal in the United States and carry a $2,500 fine per egg?’” Sweeney said. “I actually laughed.”

But it was no laughing matter when Sweeney and Loo were led into a detention centre with a card listing their infraction.

It read “Kinder.”

The couple says they were held for two and a half hours as they pleaded their case. Though they were eventually let off with a warning, it was an experience neither will likely forget.

“The ‘Surprise’ was the worst part of it,” Sweeney said.

According to a U.S. Customs and Border Protection release issued shortly before last Easter, the eggs “may be cute” but are considered too dangerous for kids.

“While sold in many countries, this product is banned from the U.S. because young children can choke on it,” the release read.

The agency says it seized more than 60,000 Kinder eggs from travellers’ baggage and from international mail in the 2011 fiscal year.