Deputy Chief Constable Sara Glen told journalists in a remote media briefing on Wednesday that the law does not allow fixed penalty notices to be issued to under-18s.
Between March 27 and April 13, 39 of the fines were wrongly issued to children by police in England.
During the period a total of 3,203 fines were issued by police forces in England. Over the Easter weekend there were 290 in Wales.
Members of the public as old as 100 were slapped with a £60 penalty, that is reduced to £30 if paid within two weeks.
A third of the fines went to those aged 18-24, with a further third going to those aged 25-34. In total 26 people aged between 65 to 100 also received notices.
Police said that 83 people were brought straight to court for allegedly breaking the rules.
A number of mistakes have been made in applying the sweeping new laws.
British Transport Police wrongly fined a 41-year-old woman £660, while the Metropolitan Police admitted a 21-year-old man was wrongly convicted and fined and the charge has since been set aside.
Warwickshire Police said on Tuesday five outstanding charges brought under the laws which are yet to go before the court would be dropped; while Greater Manchester Police apologised after a man was threatened with spray and arrested as he dropped off food for vulnerable family members.
South Yorkshire Police apologised for a "well-intentioned but ill-informed" exchange in which an officer appeared to tell a family they were not allowed to play in their own front garden.
Cheshire Police previously said in a tweet it had issued summonses after "multiple people from the same household going to the shops for non-essential items", but later admitted this part of the social media post was an "error".
Northamptonshire Police Chief Constable Nick Adderley said officers would start checking supermarket trolleys if people did not adhere to lockdown rules, but later backtracked and the Home Secretary said the measure was "not appropriate".
And Cambridge Police insisted it was not monitoring what people are buying from supermarkets following comments by an "over exuberant officer" on non-essential shopping aisles.
National Police Chiefs Council chairman Martin Hewitt admitted there had been a "very small number" of errors but insisted "tens and tens of thousands" of encounters with the police had been appropriate.
The new laws came in at "great speed" and police officers were "trying to do their best in very, very difficult and unusual circumstances."
He said: "We will say sorry if we got it wrong.
"Of course there have been mistakes and I think we have been very quick to come forward when we have made mistakes.
"But I would like to think that the public would have some recognition of the fact that this is legislation that came in at high speed a few weeks ago, is highly, highly unusual and we are having to adapt to that across the whole of the service.
"Whenever there have been any incidents where something was done that was not how it should have been done we will rectify that.
"I think we have been absolutely clear and upfront about rectifying any mistakes that we have made."
Ms Glen, the NPCC lead for charging and out of court disposals, said a 5% "human error rate" is factored into data when measuring performance, but the number of mistakes under the new laws is "way below that" and the "vast majority of officers are getting it right".
The National Police Chiefs' Council gave a force-by-force breakdown of the number of penalty notices issued, with the highest in Lancashire where 380 were handed out.
Thames Valley Police chalked up 219, while Surrey issued 205.
Ms Glen said visitors to the seaside town of Blackpool may be why Lancashire's tally was so high.
"We absolutely see temperatures and coastal resorts having a challenge there," she said.
"If we look at Lancashire, they had a phenomenal... 4,853 calls for service.
"They needed to issue 380 fines - very much due to barbecues, house parties... Blackpool, beaches, you've got a lot going on there in terms of temperature, location, context."
She said in England there were 398 enforcements last Friday and 424 on Saturday, when the country widely saw temperatures of above 20C, before a drop to 177 on Monday as the weather turned cooler.
Sussex Police Chief Constable Giles York said that his force had fined sunseekers who had travelled more than 100 miles to the coast for a day out.
Those punished included a family who came from Birmingham to Brighton; another who went from St Albans to Camber to go for a walk on the beach; and a couple who travelled from Hemel Hempstead to Eastbourne because they heard the view was nice.