When the children recovered, the family returned to the lake on December 29, but hours later Ms Lake's son also started vomiting.
"If we had known there was even a remote chance these kids were sick because of the lake there is no way we would have taken them back for a repeat performance," Ms Lake said.
Last week Ballina Shire Council notified North Coast Public Health of complaints that people believed they had become ill after swimming in the lake in early January.
Council's Regulatory Services group manager Rod Willis said waterways contained more nutrients after rain.
"We do caution people not to swim within three days of heavy rain, and that applies to people swimming in beaches, estuaries and Lake Ainsworth."