Richard Newton had babysat for the child before contacting her on line and making a series of lewd suggestions to her.
The 29-year-old also got the troubled schoolgirl to send him pictures of herself with nothing on.
Newton, who at the time had links with the Malmesbury area, had met the youngster and her family through a help group for people with learning disabilities, Swindon Crown Court was told.
Newton, now of Cheltenham, pleaded guilty to three counts of causing or inciting a child under 13 to engage in engage in sexual activity.
Colin Meeke, prosecuting, said indecent images were first found on the child's phone in October 2015, but she refused to say who she had been contacting.
A year later the police were investigating another matter when she revealed the communication with the defendant.
Mr Meeke said there were huge chat logs from Kik Messaging where he had been asking the girl to do things on-line for him.
And though the images could not be seen by investigators he said there was evidence that they had been sent by her at his request.
At one point he said Newton feared someone was going to examine her tablet and told her 'just delete everything naughty, ok'.
Tony Bignall, defending, said his client had no previous convictions and suffers from learning difficulties, being mildly autistic.
He said Newton operates at an age lower than his own and the offending took place a long time ago, in autumn 2015
Jailing him, Judge Jason Taylor QC said "It is clear it has had an affect on her and the family.
"The fact of the matter is this has had massive ramifications for trust and security. It has affected the relationship between mother and daughter.
"The child has been experiencing feelings of guilty she should never have to feel, as she was the child and you the adult.
"You prioritised your own sexual gratification over this girl's welfare."
He must also register as a sex offender for life and abide by the conditions of a sexual harm prevention order.
An NSPCC spokesman said: “Newton targeted and exploited his victim in a deplorable way for his own sexual gratification.
“Children with learning difficulties are amongst the most vulnerable in society and should be protected from such heinous forms of abuse.
“The NSPCC is committed to working with the victims of child sexual abuse and helping them rebuild their lives.”
Any young person can contact Childline on 0800 1111 or childline.org.uk. Adults concerned about a child’s safety can contact the NSPCC Helpline 0808 800 5000 or nspcc.org.uk. Both are free, confidential, and open 24/7