Gilbert Arenas is about to lose access to his 4 children if his baby mama has her way ... and it's all over a 15 second video of their 8-year-old son on the hood of a moving vehicle.
Gilbert told us he got an email from Laura's people saying they were going to try and take custody away from him, and TMZ Sports has learned he told the truth.
Our sources say Laura -- who currently has primary physical custody -- will go to court and ask the judge to significantly reduce Gilbert's visitation. She also wants the judge to impose safeguards so the kids aren't put in dangerous situations.
As one Laura source put it, "This is just the straw that broke the camel's back. He's done many other things."
In case you didn't know, Gilbert and Laura have been at war for several years, and it's getting worse ... or as one source put it, "ferocious."