Two Mexican children were being taken into the care of social services last night after they were intercepted at Heathrow with 15 kilograms of cocaine strapped to their legs.

A Mexican woman, believed to be their mother, who was stopped with the 11-year-old girl and 13-year-old boy, was being questioned by Customs officers about the drugs haul, estimated to have a street value of £675,000.

Revenue & Customs said that the case revealed the depths that people would plumb to smuggle illicit drugs into Britain.

The three were intercepted at lunchtime on Tuesday as they passed through Terminal Four after touching down on a British Airways flight from Mexico City. It is understood that no drugs were found on the woman.

Bob Gaiger, a spokesman for Revenue & Customs, told The Times that children were sometimes used as a cover by people trying to smuggle drugs through British airports. “We have had drugs hidden in disposable nappies being worn by a baby, or drugs being hidden in a buggy.

“To have drugs strapped to their legs is extremely unusual. For young children to be used in this way, it’s a horrendous thing to do.”

Mr Gaiger said that the woman who was stopped with the children had claimed to be their mother but that this was yet to be confirmed.

Interviews with the trio were continuing last night, although the process was slow because interpreters were required.

A decision on whether to charge the woman with drug importation offences is expected to be made today.

The fate of the children was unclear last night, although Mr Gaiger confirmed that social services were trying to find them a foster home as a “temporary measure”.

He would not rule out the option of the children being charged since there was provision under the law for prosecution.

Mr Gaiger said that the group had been stopped as “part of routine searches of arriving passengers”.

“The group was stopped and questioned by officers. The drugs were discovered when the individuals and their baggage were searched.

“We never cease to be amazed at the lengths to which some people will go to hide drugs from us when they pass through our controls.

“Revenue & Customs is working at the forefront of the fight to stop drugs entering the UK and to reduce the associated harm to our communities. We aim to protect society from this activity wherever we detect it.”

Last night British Airways refused to comment.

The authorities have reported that British gangs use infants in a variety of ways for smuggling, including hiding illicit drugs in jars of baby food.

Another method used by drug smugglers was to create an “artificial family”, Mr Gaiger said. “They look like a family coming back from holidays, when it is really a man who has persuaded a woman and her children to go on a trip — to paint a picture, like a bluff, which looks innocent but is anything but.”

Such schemes are not limited to children. Last year, packets of cocaine were discovered inside a labrador. The haul was spotted by an X-ray machine at Heathrow.

The Independent Police Complaints Commission recommended last year that Customs officers be given more training to detect carriers after a woman got through airport security but died when packets of cocaine burst in her stomach.

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