Lucy Jarrett: "Our children have grown up together"
England's Children's Minister wants a review of the case of two police officers told they were breaking the law, caring for each other's children.
Ofsted said the arrangement contravened the Childcare Act because it lasted for longer than two hours a day, and constituted receiving "a reward".
It said the women would have to be registered as childminders.
Minister Vernon Coaker said his department was talking to Ofsted about this particular case.
The two detective constables, Leanne Shepherd, from Milton Keynes, and Lucy Jarrett, from Buckingham, told the BBC how Ofsted insisted they end their arrangement.
Ms Shepherd, who serves with Thames Valley Police, recalled: "A lady came to the front door and she identified herself as being from Ofsted. She said a complaint had been made that I was illegally childminding.
"I was just shocked - I thought they were a bit confused about the arrangement between us.
"So I invited her in and told her situation - the arrangement between Lucy and I - and I was shocked when she told me I was breaking the law."
Reward is not just a case of money changing hands. The supply of services or goods and, in some circumstances, reciprocal arrangements can also constitute reward
Ms Jarrett added: "Our children were never in any harm, they were never in any danger.
"To think that they would waste their time and effort on innocent people who are trying to provide for their families by returning to the workplace... Surely their time and effort would be better placed elsewhere."
Thames Valley Police Federation, which represents rank-and-file officers, said the pair had its "full support".
Secretary Andy Viney said: "Both of them are experienced professional officers.
"They just want to return to work after having children and have found that the system is working totally against them.
"They've been threatened with prosecution by Ofsted if they continue doing this."
An Ofsted spokesman said it applied regulations found in the Childcare Act 2006, but was currently discussing the interpretation of the word "reward" with the department for Children, Schools and Families (DCSF).
"Reward is not just a case of money changing hands. The supply of services or goods and, in some circumstances, reciprocal arrangements can also constitute reward.
"Generally, mothers who look after each other's children are not providing childminding for which registration is required, as exemptions apply to them, for example because the care is for less than two hours or it takes place on less than 14 days in a year.
"Where such arrangements are regular and for longer periods, then registration is usually required."
Close relatives of children, such as grandparents, siblings, aunts or uncles, were exempt from the rules, he added.
Ofsted only operates in England, so this interpretation of the law on child care for "reward" applies to England rather than elsewhere in the UK.
Michelle Elliott, director of the children's charity Kidscape, told the BBC's Breakfast programme that the decision defied common sense and would impose extra childcare costs on families.
She added: "These children were looked after in a secure environment with people that they knew.
"There must be thousands of people out there who are doing the same thing who are now going to think: 'Do I have to spend £300 a week or whatever it is?'"
Minister for Children, Schools and Families Vernon Coaker insisted the Childcare Act 2006 was in place "to ensure the safety and wellbeing of all children" but the government needed to make sure it did not "penalise hard-working families".
"My department is speaking to Ofsted about the interpretation of the word 'reward' in this particular case," he said.
A petition to scrap the rules governing reciprocal child care on the Number 10 website had gathered more than 5,300 signatures by 0530 BST on Monday.
Anyone required to register to become a childminder would also have to undergo a criminal records check.
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