Twins Drown in Back-Yard Spa Accident : Accident: Miscommunication between parents and a baby-sitter resulted in the 21-month-old youngsters being left unsupervised for a few minutes at the Laguna Niguel home, authorities say.

Twin toddlers drowned in their parents’ back-yard spa in Laguna Niguel on Saturday evening after they were left unsupervised for a few minutes, authorities said.

An investigator for the Orange County coroner’s office said David Lam and his twin sister, Diana, 21 months old, were pronounced dead at Mission Hospital Regional Medical Center in Mission Viejo about 5:30 p.m.

The drowning occurred after an apparent miscommunication between the twins’ parents, Minh and Constance Lam, and a live-in baby-sitter, each of whom thought the other was watching the children at the Laguna Niguel home.

“All I can say was there was some misunderstanding among the adults and nobody was watching the twins,” Ted Sullivan, a senior coroner’s investigator, said. “This is what happens in 99% of all drownings involving infants.”

Pool drownings are the leading cause of accidental death for Orange County children, statistics show. Six children under 4 years of age drowned last year and three toddlers have drowned so far this year.

As recently as last week, a 2-year-old girl pulled from the bottom of a back-yard swimming pool was declared brain-dead, about 24 hours after her 3-year-old brother drowned in the same accident.

In those cases, the toddlers apparently opened a sliding glass door while their mother slept and wandered into the pool. They were found lying on the bottom.

Those drownings sparked renewed warnings to parents to keep an especially close eye on children, particularly during the warmer spring and summer months.

In 1991, eight children drowned in Orange County, six of them in swimming pools. Nationwide, 90% of drownings involving children 4 and under occur at homes. All cities in Orange County require fencing around three sides of a pool, but no fencing is required between the pool and home.