False allegation

[MenTeach: We receive letters from people and unfortunately can be common. Do you have advice?]

I have a friend of a friend who has a son (25 years old and recently married) who is a day care teacher and has been wrongly accused of something two years after the event. This supposedly happened to a 4 or 5 year old who after driving by a school she used to attend where this person worked, remembered this event.

Can you give me any advice or tell me where to go for help?