On Monday, the actress, 45, proudly shared the sweet message that her 5½-year-old Samuel tried to leave anonymously at the local library.
“When the librarian finds a love note your son tucked into a picture book,” Garner wrote on Instagram along with a photo of her youngest child’s message that read: “Hello, You are loved. I believe in you.”
Garner and ex Ben Affleck are also parents to daughters Violet, 12, and Seraphina, 9.
In addition to leaving little a “love note,” the pair’s little one also has an interest in superheroes and has taken a liking to one of Batman’s teammates more so than his dad’s Caped Crusader.
“My son does love The Flash,” the Justice League actor admitted in November. “He feels that he’s very fast, and he likes to demonstrate that.”
Another character who influences Sam’s need for speed? Dash, the middle child from The Incredibles. “That’s who he wants to be,” Affleck explained.
Despite their split, Garner and Affleck have remained amicable and continue to co-parent their kids.
The parents of three came together to celebrate daughter Seraphina’s 9th birthday party at their Los Angeles home on Jan. 6.
In addition to spending Christmas Day together as a family, they were spotted taking a morning stroll together in Los Angeles in December and got together for Thanksgiving as well. Affleck capped off that holiday by taking his daughters to see the hit musical Hamilton.
This article originally appeared on PEOPLE.