The toddler's mother, who cannot be identified for legal reasons, said she had let her Dunn take care of her child on three occasions because she had been finding it difficult to cope.
She said: "I felt like he was a support at that time."
She left her child with Dunn, of Hamilton, South Lanarkshire, on the day of the assault while she visited a friend, the court heard.
The mother later received contact saying the girl had bumped into her buggy and had a bleeding nose.
He sent a message to her, which read: "I'm just raging as I thought she was chilling watching Paw Patrol then I heard the thud."
Dunn, who denied hitting the girl, later contacted the girl's mother to say he was taking the child to a minor injuries unit because she did not seem well after her nap and was "flopping to one side". He also said he noticed a small lump on her head.
An ambulance was called and an examination at hospital revealed two fractures to her skull.
Dunn's defence advocate Niall McCluskey said the tumble dryer incident had been a "stupid piece of tomfoolery", although he added that he did not wish to diminish the charge.