'Okay Baby' TikTok Star's Mom Shares Detailed Explanation of Fatal Crash

"Okay Baby" social media star Preston Ordone's mother is sharing details surrounding the crash that ended her son's life ... and, she's maintaining his car seat was secured in place properly.

Katelynn Ordone shared more details about the accident last month ... starting by thanking everyone who has kept up their support for the family -- before revealing she and her husband, Jaelen, were so severely concussed in the Louisiana crash they remember nothing about it.

To determine exactly what happened, Katelynn says they hired an "independent accident reconstruction expert to thoroughly review the incident."

According to Ordone, their car smashed into a tree at 60 MPH during the single-vehicle crash ... but, she says the investigator found Preston was properly secured into his car seat when the impact occurred.

Ordone claims Preston was removed from the car, still securely fastened in the seat -- and brought to the side of the road by bystanders before first responders arrived at the crash site at least 15 minutes later, at which time he was handed over to them in his car seat.

While Katelynn says Preston was secured correctly in the car seat, she admits "there appears to have been an issue with how the seat attached to the base." Ordone claims -- after doing some research -- she found other parents have complained of similar issues.

As you know ... Preston died in a car crash on April 24 after the 2011 Ford F-150 pickup truck in which he was riding with his parents veered off the road and hit a tree.

While cops initially believed Preston wasn't properly secured in the car seat, the family has always maintained he was ... a trend continuing with Ordone's latest post.

Preston was just 2 years old.