Steven Hirschorn said his son Ollie was upset when he lost his lion, Liley, at Hughenden Manor in Buckinghamshire.
However, the toy was returned last week along with a photo diary showing Liley driving a buggy and exploring the National Trust property.
Mr Hirschorn said it was "a lovely gesture".
Ollie has had Liley since he was about 11 months old and is so treasured that a back-up had already been bought, in case he ever got lost.
Mr Hirschorn said although the two lions look identical, Ollie could tell the difference and was sad when "good Liley" went missing on Easter Monday.
"He was on the verge of tears when it was pointed out that he wasn't holding Liley," Mr Hirschorn said.
Staff at the former home of Prime Minister Benjamin Disraeli were told of the missing lion, but he remained unfound until two days later.
Charlotte Russell, conservation assistant, said: "He was found in one of the boxes we have on the top floor, it wasn't an obvious place.
"Our office thought it would be a nice idea to take photos of him in different places around the manor - so the boy could see he had had an adventure."
Mr Hirschorn, who lives in west London, said he was impressed by the effort, having thought Liley would be sent back "stuffed in an envelope".
"Straight away Ollie was playing with the stickers they sent and we've told him the story shown in the photos.
"He was very happy to see Liley again."
A three-year-old boy has been reunited with his favourite toy lion, which was photographed having an "adventure" at a stately home after being lost.