The online post says 10-year-old Kathryn Schmidt of Batavia died last Friday, along with her two young cousins.
Jonathon Schmid, the page's creator, says the funds raised will help kids who can't afford sports, or who want to adopt animals.
A fundraiser for 7-year-old Abigail Oswald and 6-year-old Caleb Oswald, the other two children killed, has already pushed past $200,000.
The children's Wheaton family also plans to donate the money in their memory.
The kids were with their family, wearing life jackets on the boat, when a storm hit last Friday.
The National Weather Service confirmed that winds reached up to 100 mph during the storm.
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