The 40-year-old British actor dedicated a sweet message to Kerr on Instagram to mark the Australian model's 34th birthday.
"#HAPPY BIRTHDAY to an amazing mother co-parent and friend," he captioned a photo of their son's homemade sign reading, "I [love] u mum."
Bloom and Kerr split in 2013 after three years of marriage, but continue to co-parent their 6-year-old son, Flynn. The actor has since dated singer Katy Perry, while Kerr got engaged to Snapchat founder Evan Spiegel in July.
"Our son is our priority, so you have to come from love. You have to be kind," she said of her relationship with Bloom in a January 2016 issue of Net-a-Porter magazine.
"Orlando thinks [Evan is] great," she added. "We're just a modern family now!"
Bloom had warned Kerr in August 2016 before photos surfaced of him paddleboarding nude with Perry. He recently said in the May issue of Elle U.K. that he was "feeling free" during the incident.