The 41st president shaved his head to show solidarity with Patrick, a 2-year-old battling leukemia. Patrick is the son of one of the president's Secret Service members, the Bush Protective Division.
The 89-year-old made the decision after seeing other members of his Secret Service team with shaved heads.
The security detail launched a website to help with expenses associated with Patrick's treatment. The former president made a donation.
George and Barbara Bush lost their second child, 4-year-old Robin Bush, to leukemia almost 60 years ago.
The Associated Press contributed to this report.