The service at Calvary Chapel Yorba Linda was not open to the public to attend but was livestreamed for viewing online.
"This a a memorial, not a funeral," Pastor Joshua Holiday said. "A funeral's a ceremony, it's held in connection with the burial or cremation, someone's death and it signifies the end of their existence. A memorial service is a ceremony serving to preserve the remembrance of someone's life. The focal point is different.
"We're here to celebrate the life of Aiden," he added.
Joanna Cloonan, the boy's mother, eulogized her son in an emotional tribute. She opened her remarks by expressing gratitude for the outpouring of support from loved ones and strangers alike.
"Your kindness, your prayers, your support and unbelievable generosity has helped provide me with so much strength, so I may stand on my own two feet today, in front of you, and share the beauty of who Aiden was and still is," Coonan said.
CHP releases image of car involved in fatal road-rage shooting of Aiden Leos in OC
"The joy he brought into our lives was insurmountable," she said. "My heart melted every time he laughed."
Aiden was killed May 21 while his mother was driving him to kindergarten. Cloonan was driving a silver Chevrolet Cruze sedan with her son in the right rear passenger booster seat when another driver opened fire between 7:55 and 8:15 a.m. on the northbound 55 Freeway between the 22 Freeway and Chapman Avenue.
The boy was rushed to Children's Hospital of Orange County, where he was pronounced dead.
The California Highway Patrol later released the photo of the suspect vehicle, described as a white 2018 or 2019 Volkswagen Golf Sportswagen with non-tinted windows and a sunroof.
Investigators have not been able to obtain a license plate from the snapshot. The suspect vehicle was last seen heading eastbound on the 91 Freeway toward Riverside, said CHP Officer Florentino Olivera.
Officials believe a woman was driving the vehicle and a male passenger was sitting in the front seat.
MORE | 'Mommy, my tummy hurts': Aiden Leos' sister describes little brother's final moments
The reward fund grew to $500,000 on Thursday, according to Orange County District Attorney Todd Spitzer and the website aiden-reward.com, which gives details of the case, a photo of the suspect vehicle and information on how to submit tips.
"I want nothing more than to find justice, although it won't bring you back into our arms," Aiden's mother said during her eulogy. "It makes me outraged that such a precious beautiful soul did not get the opportunity to continue developing into a young man, and starting a family of his own one day, while accomplishing his heart's desires. My precious son had his life ripped away from him for absolutely no reason.
"They took his life, and my heart along with it," she said.
In lieu of flowers, the family has requested that supporters make donations to assist the family through a pair of GoFundMe pages.
Anyone with information about the case is asked to call the Highway Patrol at (714) 567-6000. The CHP has also set up the email@example.com email to receive tips. Anonymous tips may also be phoned in to (800) TELL-CHP.
City News Service contributed to this report.