After a 12-month battle she was granted custody by the High Court in London and agreed to let the children visit Paco twice a year. But a few days before they were due to return from their first visit, Paco rang to say they would not be coming home. It was nearly a year before she saw her children again.
The number of children being abducted by one of their parents following a divorce has increased by 58 per cent since 1995. And now one of only three or four organisations in Europe that works to bring them home is facing closure.
Reunite, formed in 1986 to help parents recover children who have been taken abroad, may have to close by the summer unless it can urgently raise funds.
The organisation helped Ms Mainstone find a solicitor and advised her on the Spanish legal system, enabling her to win her children back. Ms Mainstone, aged 29, met Paco 10 years ago shortly after she started work in a bar in south-east Spain. They married in April 1989 - two days before her twentieth birthday - and Jessica was born two months later. Dawn settled into a new life and 17 months afterwards she had Laura. "I was happy with Paco, although he was very often out till late," she said.
"Then one day I walked into the house and found him injecting himself with heroin. I had had no idea, I had never been around drugs ..." Paco promised that it was a one-off and Ms Mainstone stayed with him. Francis was born in 1994 and then she discovered that her husband had sold all the baby's nappies to pay for his habit.
She saved up her child benefit and returned to England. Paco started proceedings at the High Court and Ms Mainstone knew that under the terms of the Hague Convention, the children would have to return to Spain and she would be charged with abduction. She persuaded him to drop the case and immediately sued for and won custody. Then Paco took the children.
"I got in touch with Reunite who helped me with the court case in Spain but the authorities said the children had been born over there and they had to stay, despite the fact that Paco was a drug addict. Reunite helped me to find a solicitor ... finally I was granted custody."
It was just one of many cases that Reunite deals with every year. Denise Carter, the director, said: "Last year we dealt with 230 cases involving 338 children but there are probably twice as many as that."
Ms Carter, who joined Reunite after fighting a custody battle over her own children in the United States, said the problem was growing as the number of cross-cultural marriages increased. "The classic example is the holiday romance which goes wrong and the mother finds herself trapped in a bad marriage in a foreign country.
"If she leaves her husband and returns to Britain with the children, she is breaking the terms of the Hague Convention, which states that a child must return to the country in which it was originally resident. Once the child has been returned, the mother is left fighting to get her children back. She has no representation in a foreign country, fighting a legal system she doesn't understand."
Reunite advises parents on how to find their children and works with detective agencies and lawyers to help them through a custody case. But unless the charity can raise more money, it might have to cut back on its services or even close.
Ms Carter said: "We receive pounds 40,000 from the Government but last year we spent pounds 103,000 ... We have asked for National Lottery money twice and been refused each time and I cannot see us ever fitting the criteria so that we can qualify for a grant. We are desperately trying to keep our doors open for the parents but I am not sure how much longer we can keep going."
Bill Olner, chairman of the all-party group on child abduction, said: "We are fighting to get more money for Reunite but it seems that child abduction is an issue that often gets pushed down the agenda. The problem is increasing and we need to build up a network of similar organisations across Europe, rather than have to fight to keep this one open."Reuse content