An Illinois couple whose two young kids tragically drowned after their boat capsized during a massive storm that ripped through Wisconsin’s Geneva Lake were “lifelong, experienced boaters,” friends and authorities said.

Caleb Oswald, 6, and Abigail Oswald, 7, “were more than brother and sister—they were best friends,” wrote the tots’ father, Brad Oswald, on a charity Gofundme.

“They filled our home with laughter, music, hugs, and endless love. They were deeply loved by their family, friends, teachers, and everyone who had the privilege of knowing them.”

Investigators determined the children, whose names were released this week, died by drowning, with no signs of external injury — after Walworth County was slammed with a “sudden and severe” storm on July 3.

A 10-year-old unidentified girl was also killed when the boat capsized — leaving six adults and one child as survivors — as peak winds topped out at an estimated 90-100. mph, according to Fox6 Milwaukee. 

Local law enforcement described the unidentified 47-year-old boat operator as having “extensive boating experience” yet he was unable to find refuge before the storm hit. 

“These are dear friends of mine,” wrote Samantha Foster on Facebook about Brad Oswald and his wife Erica.

“They were lifelong, experienced boaters, on a vessel well within its capacity, and every child was wearing a life jacket.”

Two large waves swamped the 25-foot boat and a third, fatal wave then capsized the vessel, sending it to the bottom of the lake.

As of Wednesday afternoon, over $110,000 had been raised through the Gofundme, which the Oswald family does not plan to keep for themselves.

The funds will “be donated to support children and families through a charitable organization, ensuring Caleb and Abigail’s memory continues to make a positive difference in the lives of others.”