The Willow Tree
by Jane Rice
By my count, this is the fifth time travel story in the February 1959 issue of
F&SF, which is a record. Maybe they were anticipating the release of The
Time Machine in the subsequent year.
In this story, four orphans are sent to live in the past with the rather odd Aunt Martha and the slightly less odd Aunt Harriet, who together give the children only one commandment: Never play under the willow tree!
When the four O 
“The Willow Tree” by Jane Rice, Magazine
of Fantasy and Science Fiction, February 1959.