I had Marines shoot children = I ordered Marines to shoot children?

Wake up

yes.

Can also have another (a secondary, imo) meaning, e.g.

"I had three pupils come to me yesterday, each upset because he had lost his bus fare home."

But in this case, it was probably a direct order. The marines had to shoot at the car.

It's a very informal figure of speech.

In this case, "I had" means "I have known about" or "there have been times where" or "have had under my command."

Sometimes when a person is speaking of events in the past, they may say, "I've had . . . " as in "I've had several boyfriends, but now I am married." or "I've had people come up to me and ask me for directions."

I do not believe that it means this speaker ordered any shootings. The military procedure/orders/ rules may have been to shoot any car that did not stop on command. To find out later that the car contained families was very upsetting.

So in his unit, he has "had" (soldiers under his command where this has happened)

Yes I agree. Punkey is right. May I change my answer? The interviewee is probably referring to the fact that these things happened, not that he actually ordered the marines to shoot the people in the car.
To make it clearer, he should have said "I've had....."
Written the other way, it is ambiguous.

Much apreciated.

I don't believe the language supports your contention, Punkey. The lead in,

"Context:
“When a car doesn’t stop, it crosses the trigger line, Marines engage and, yes, sir, there are people inside the car that are killed that have nothing to do with it,” Sgt. Maj. Edward T. Sax, the battalion’s senior noncommissioned officer, testified. "

certainly indicates "I had" could mean a direct order to shoot to kill.

It's not like it's a first instance. The US has a long and storied history of gunning down innocent civilians. You don't get to the high single digit millions of dead from troops who care who their targets are.

Remember the Apache helicopter murderers - something like " Serves them right for bringing their kids to a fire fight" - truly caring individuals.

Welcome back, JTT.

PUNKEY is correct, regardless of JTT's rant.

How is Punkey correct, Merry? Is she correct in describing this as a "figure of speech"?

Go ahead, Merry, explain.