William Tiojai was attending a party with several other children when the incident happened. A 12-year-old boy found William and brought him to the surface after realizing the young boy was in trouble.
An off-duty border patrol agent performed CPR on William after he was removed from the pool.
William died at Children's Medical Center Dallas at about 6 p.m. Saturday, authorities said.
DeSoto police said the children were under adult supervision, but the victim's parents were not poolside at the time.