The considered safe exposure is about one milligram per kilogram bodyweight, so your children should be fine gargling on about 20 to 50 milligrams of the stuff

The considered safe exposure is about one milligram per kilogram bodyweight, so your children should be fine gargling on about 20 to 50 milligrams of the stuff without issue (somewhere after that you reach norminal toxicity where it'll just kill you normally like 99.999% of the pesticides out there).