"Back today for a long day of chemo," the 52-year-old magician captioned Thursday's images of him lying next to his child and giving him a kiss on the cheek.
People.com said Johnny -- now 5 -- was first diagnosed with leukemia in 2015 and has only had one brief remission from the disease since then.
"He is an amazingly strong little boy, and with the support of family, friends, and my loyal fans we look forward to the day he is again in remission," the family said in a statement to Entertainment Tonight earlier this month when they learned Johnny's cancer had returned. "We want to thank you all for the outpouring of love, good thoughts and prayers for our amazing boy."
