Meg Burgess was killed when a wall designed by George Collier and constructed by his company, Parcol Developments, collapsed onto a footpath in Ffordd Penrhwylfa, Prestatyn, north Wales, in July 2008.
Collier, 49, of Kinmel Bay, Conwy, who denied the charge during a three-week trial at Mold Crown Court, was also disqualified from being a company director for seven years.
The firm, of which Collier was a director, admitted health and safety charges but no separate penalty was made.
Meg was walking home from the shops with her mother when she died.
During the trial the jury heard that as they walked along the pavement next to a cottage which was being renovated, a newly built 5ft concrete block garden wall collapsed onto Meg.
Collier denied responsibility and said the wall was a garden wall, not a retaining wall, built by two bricklayers.
He also denied prosecution claims that he put so much soil behind the wall that it collapsed under the pressure.
The prosecution said Collier, who had 30 years’ experience, should have realised that it was a retaining wall.
In a statement issued at the time of the toddler’s death by North Wales Police, Meg’s parents Pete and Lindsay Burgess said: “Meg was such a special girl. She knew how people felt and brought so much happiness to those who needed it.
“She was best friend to Mummy, Daddy and her brother Wilson. She loved to hold our hands, sing, smile and have all the fun in the world.
“We love you, Meg, you taught us how to live our lives. Thank you.”
They said their daughter’s eyes and heart would be donated.