Merlin Toomer, who is under assessment for autism and suffers from high anxiety, lost the wizard toy, also called Merlin, at Yorkshire Wildlife Park.
His mum Zara has issued a Facebook plea for the return of the toy.
She said: "We are offering a Â£200 reward. He has had him since he was born and means the world to him."
The family say the toy was lost near the bush pig and lemur enclosure at the visitor attraction on Saturday.
She added: "He was gone within ten minutes of going to look for him. If anyone has picked Merlin up can you please get in touch."
Anyone who can help can contact us at [email protected] and we will pass messages onto the family.