Blademir Viveros, 27, was charged with two counts of manslaughter and one count of aggravated assault.
His bond has been set at $250,000 for the two manslaughter charges and $300,000 for aggravated assault: $800,000 in total.
Authorities say Viveros had responded to a robbery in progress call, where he struck the victims on June 20.
ORIGINAL REPORT: 16-year-old 'died on his birthday' when Missouri City police car hit him and his mom, dad says
According to police, a man armed with a handgun approached a victim and stole $200 before fleeing in a silver Honda Civic.
Meanwhile, Viveros was heading east when the Stewarts pulled out of a Dollar Tree parking lot. That's when the officer T-boned their vehicle, police said.
Both the mother and her son, identified as 53-year-old Angela Stewart, a Houston school counselor, and her 16-year-old son, Mason Stewart, died at the scene.
Officials said Viveros was driving over the posted speed limit, and did not have his emergency lights on.
Family members told ABC Houston affiliate KTRK that the crash happened on Mason's 16th birthday.
On Wednesday, Attorney Jack Nugent shared the following statement from the Stewart family.
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"We are still grieving and heartbroken beyond words by the tragic and senseless loss of our beloved wife, mother, brother, and son. Angela and Mason were taken from us far too soon by the actions of a police officer that shocked the conscience. Today's indictment is just the first step towards accountability and should only be the beginning of holding the officer responsible for his wrongdoing. It does not heal the pain we feel every day. We extend our deepest gratitude to those who continue to support us in this hard time. We hope our struggle serves as a constant reminder that life is precious, and that justice is necessary. We will continue to honor Angela and Mason's memory and support any action taken that will help in any way to prevent others from enduring this kind of devastating loss."
The DA's office said that Viveros' court date has not been set.