First things first: Don’t go accusing anyone. Remember, ideas travel and it’s a common thing for multiple people to have similar ideas at the same time.
Second, who have you told your idea? Your family? Your critique group? Your best friends? The other parents at the PTA meeting?
The truth is, ideas can’t be stolen. Ideas are not products or “works.” They are simply mental energy that has not made it from the brain to the prototype stage.
That being said, did you know that ideas travel? They do! As a professional reviewer there have been seasons when I’ve reviewed five or more books about basically the same subject, and yet not one of them was exactly like the other.
Think of it this way: All humans have similar experiences. They only become singular when they are told from YOUR perspective.
Hope this helps!