Judge William Wickham, at Liverpool Crown Court, said the sentence, the maximum he was allowed to impose on Andrew Ellis, 15, was 'derisory and inadequate, as Parliament has belatedly recognised'.
He told Ellis, who admitted causing death by dangerous driving: 'You have escaped a long sentence, which you deserve, by a few hours.'
Ellis, from Huyton, Merseyside, was banned from driving for 10 years. He had never driven before when he reversed at speed near his home and killed Kevin Downes on 15 August. The next day the maximum sentence for causing death by dangerous driving was raised to 10 years.
When the accident happened, Kevin was walking with his brother Sean, 6, and their babysitter Sandra Cairns, 15, who was carrying a baby. Elizabeth Cliff, for the prosecution, said that Ellis and two companions had been using the vehicle as a 'plaything' after it was abandoned by other youths when it ran out of petrol.
'The vehicle was being raced up and down Pennard Avenue and they were taking it in turns to drive it. It was being revved, screeching to a halt and doing wheelies,' she said.
The car, driven by Ellis, reversed round the corner as he put his foot on the accelerator and it collided with the victims as smoke came from the tyres.
Kevin died instantly from head injuries. Sandra was trapped against concrete posts and suffered a broken ankle. She had the presence of mind to hold up Charlotte, the 10-month-old baby, as the car hurtled towards them and the baby suffered only superficial abrasions.
Deborah Gould, for the defence, urged the judge to impose a supervision order. She said Ellis would be released from custody after six months, whereas he could be under supervision of social services for three years and given counselling and specific assistance.
He was very remorseful and his family was hounded out of the area because of local reaction, she said.
'He had never driven before. Egged on by the others, he put himself behind the wheel and decided to have a go,' she said.
Two other youths who pleaded not guilty to aiding and abetting Ellis in causing death by dangerous driving and aggravated vehicle taking have been released on bail and face trial in February.