The lawsuit was filed in federal court in San Diego on behalf of 13 people aboard the 26-foot Sea Ray boat that was hit by the Coast Guard vessel Dec. 20 during the San Diego Bay Parade of Lights. Anthony DeWeese, 8, died in the crash.
The DeWeeses and two other families on the boat that got hit are seeking unspecified damages for negligence and wrongful death.
"It was just totally unnecessary," said DeWeese family attorney Mike Neil.
Neil said the Coast Guard boat was apparently not on a rescue mission and "just hot-dogging" in a bay crowded with boats and kayaks during the parade. He estimated the Coast Guard boat streaked across the bay at 35 to 46 mph.
Alan DeWeese, Anthony's father, had his boat at "basically idle speed," no more than 5 mph, when he saw the Coast Guard vessel come at him from behind, Neil said. DeWeese went full-throttle to avoid getting hit, but it was too late.
Coast Guard spokesman Lt. Josh Nelson said he could not comment on pending litigation.
The Coast Guard previously promised a full investigation. The National Transportation Safety Board and the San Diego Harbor Police are also investigating the cause of the crash.