Write it down tonight, and keep writing it down.
Date, time, who was there, what was said, what you saw. Write what your children told you in their own words, in quotation marks, the same day they said it. Photograph injuries with something in frame that shows scale and keep the original file, not a screenshot.
A note written the night it happened carries weight that your memory of it will not carry two years from now. This is the single highest-value thing you can start doing today, and it costs nothing.

