Jamie Nichols, 32, of Harwood Close in Pulborough, pleaded guilty to death by careless driving while under the influence of alcohol or drugs in September.
He had crashed a car containing his fiancé and their children at Newpound Common, near Wisborough Green, on January 10.
Yesterday he was sentenced to one year in prison, with another on licence, and was disqualified from driving for three years at Hove Crown Court.
A saliva and blood test after the collision in January revealed traces of cocaine over the legal limit in Nichols’ system, which the court was told was from a house party the previous evening.
Nichols’s fiancé had written to the court to request a non-custodial sentence and said Nichols was essential to their son’s recovery.
As she delivered the sentence, Ms Barnes acknowledged Nichols’ repentance and the damage already caused to his family, who had stood by him throughout proceedings.
“To say this is tragic really doesn’t even begin to explain just how awful the consequences of your driving on that day are,” she said.
“I don’t for a moment underestimate the damage you suffered to yourself and your son, and I have huge sympathy for you and your family.
“But I can’t ignore the cocaine in your system. I don’t feel that I would be doing my duty if I did not mark this with a prison sentence.”
The court heard how, on January 10, Nichols oversteered, clipped a kerb and ‘ballooned’ into the other side of the road.
After colliding with a car and injuring the driver, Nichols’ Mazda crashed into a hedgerow.
Alongside the children’s tragic injuries – his six-year-old son can now only communicate by blinking – Nichols’ fiancé suffered leg injuries and Nichols himself sustained a ‘brain injury’.
The prosecution argued the injuries suffered by his son were ‘aggravating circumstances’ in addition to the main charge, but acknowledged the ‘relatively low’ levels of cocaine in his system.
Nichols’ defence countered that while his son’s injuries were aggravating circumstances, they were also ‘mitigating’.
Matthew Hardyman, defending, said: “What more powerful mitigating factor can there be, that as well as losing your seven month old daughter, you have also irreparably ruined the life of your son?
“He will be punished, and has been punished through living with the guilt.”
Mr Hardyman said Nichols had rarely left his son’s bedside, had learned emergency treatments such as tracheotomys to help with his recovery and was crucial in teaching him to communicate again.
Mr Hardyman said they were taking small steps forward to being a happy family unit again and asked the judge to ‘give this family a chance to heal’ by giving a suspended sentence.
Nichols’ family, including his fiancé, were distraught as the custodial sentence was delivered.
Speaking after the sentencing, investigating officer Tony Crisp, of the Sussex Police Serious Collision Investigations Unit, said: “This was the most tragic and traumatic of cases, affecting not only the lives of a close-knit family who have struggled to cope with the consequences of the crash, but also the innocent driver who was hit, and members of the public and the emergency services who stopped at the scene – many of whom were actively involved in giving emergency first aid.
“While we cannot be certain drugs were the sole cause of the collision, they may well have affected Nichols’ ability to safely drive his car.
“It goes without saying that motorists should not, under any circumstances, get behind the wheel of their vehicle while under the influence of drink or drugs. Legal limits are in place to protect all road users and to deal robustly with those who fail to adhere to the law.”