The law does not specify an age at which children can be left unattended.
Figures obtained by BBC Breakfast suggest more than 500 people were arrested in England and Wales in 2014-15 for leaving children unattended.
The majority of arrests related to children aged 10 or younger, but the ages of children involved ranged from six weeks to 15 years.
So how should parents interpret the law to work out what is legal and what might land them with a fine or a prison sentence?
The government refers parents to NSPCC guidance, which says deciding when to leave children home alone is a "tricky decision" with no "hard and fast rules" because every child is different.
It interprets the law as saying parents "shouldn't leave a child alone if they'll be at risk", and advises parents to use their judgement.
"It's safe to say babies, toddlers and young children should never be left alone, even if it's just while you pop down the road," the guidance says.
It also suggests children under 12 are "rarely mature enough to cope in an emergency and should not be left at home alone for a long period of time", while under 16s should not be left alone overnight.
A police officer told the BBC the law in this area was "woolly" and, like parents, officers had to use their judgement.
"The cop on the scene will chat with the child and see what they're like, how long they've been left and how much longer they're being left," he said.
He said a "worldly wise" 13-year-old may be fine to look after themselves after school until their parents get home, while there are 15-year-olds who "couldn't reasonably be left for more than a few minutes".
'Barely out of sight'
Tim Haines was prosecuted for leaving his two-year-old daughter alone in a car for five minutes while he went into a chemist to buy some children's paracetamol.
He said his daughter was "barely out of sight" but police were waiting at his car - and two weeks later officers arrived at his home to arrest him.
"I was taken through the magistrates' court where initially I was convicted," he said.
"My solicitor said don't appeal, I got a barrister's opinion which said don't appeal, but I was so angry that I appealed and when I finally got it in front of the judge he said 'five minutes? That's supposed to be a crime?'"
Mr Haines, who won the appeal, says the law allows parental responsibility and "they need to be able to exercise that responsibility".
Former Liberal Democrat MP John Hemming, of campaign group Justice for Families, said: "The law is up to the individual judgement of police officers or social workers and that can cause lots of problems for parents."
He said parents needed "firm advice" so they could know they were "on the right side of the law".
The Department for Education said the law was "clear that parents can be prosecuted if they leave a child unsupervised in a manner likely to cause unnecessary suffering or injury to health".
"If any child was left alone to the extent that he or she might be neglected or harmed, then the council can and will intervene," it added.
Extreme examples of children being left alone include a group of six, aged from three to 14, whose mother left them for a six-week trip to Australia. She received a suspended prison sentence.
In another case, a mother was jailed after leaving her 15-month-old daughter at home every day for a week while she went out drinking.