In his book "Keep Moving", Dick Van Dyke mentioned during the "Toot Sweets" segment, at 40 years old, he never bothered to warm up before a dance number. During filming, he felt something pop in his leg. He thought he had merely pulled a muscle, but soon after he couldn't walk without limping. He went to a doctor, who told him his whole body was full of arthritis, and within five years he wouldn't be able to get around at all without a cane or a wheelchair. Van Dyke responded to this prognosis by jumping up and dancing, which astounded the doctor. Almost 50 years later, in his brief role as Mr. Dawes Jr. in Mary Poppins Returns (2018), 92-year-old Van Dyke danced without any assistance.
The musical number 'Toy dance' involved having Dick Van Dyke on a two metre long piece of string and having puppet artists pull him around.
Lionel Jeffries played Dick Van Dyke's father, despite the fact that Dick Van Dyke is actually six months older than Jeffries.
Benny Hill was first brought onto the project to rewrite some scenes at the request of Dick Van Dyke.