Iggy | Points

Thank you so much, I've wanted to find this movie for a decade.

A movie about kids (boy and girl) becoming a friends and creating an imaginary world, and 1 day the girl dies, she tried to cross the river when it was flooding, boy went out with older lady to musieum...

When did you see this? Maybe "Eyes of a Stranger" (1981)? https://www.imdb.com/title/tt0082352/ In this one the killer wears a stocking mask.