The vandals – three younger than 10 and one aged 11 – left some of the cars in such a poor state that they could only be sold on for scrap and parts.
Others, including a Mini intended for the owner’s daughter when she turned 17, remain covered in broken glass and awaiting costly repairs.
The vandalism at Parkside Garage in Beeston also contributed to the owners having to lay off one employee and close the body shop part of the business.
But the three youngest children will face no action because of their ages, and the oldest was issued with a conditional caution last week.
Darren Idle, who runs the garage with wife Angela, said: “Do we feel angry and upset? Absolutely. We failed by the system.
“We feel like we’re not getting anywhere or getting any justice. I know that when I was 11, I knew right from wrong and my two daughters did from a very early age.
“My 13-year-old daughter has even asked the youth panel hearing if she can meet the older boy face to face to ask why he has done this.”
West Yorkshire Police said they had carried out an investigation after receiving a report of criminal damage at the garage in Ashbrooke Business Park on the afternoon of September 16.
Inspector Richard Clarke, of Leeds South neighbourhood policing team, said: “This was obviously a serious offence which resulted in a considerable amount of damage caused to the vehicles and a thorough investigation was carried out.
“Due to the young age of those involved, one of the suspects was prosecuted and received a youth conditional caution.
“Decisions on the appropriate method of dealing with young people involved in crime are considered very carefully and the Crown Prosecution Service are routinely involved at an early stage.
“In cases where the offenders are children, the opinion of specialists within the Youth Offending Service is also sought.”
Can children under 10 be charged with a crime?
The age of criminal responsibility in England and Wales is 10 years old.
This means that children under 10 cannot be arrested or charged with a crime.
However, they can be given a local child curfew or a child safety order.
Children under 10 who break the law regularly can sometimes be taken into care, or their parents could be held responsible.