As the children walked home, they saw a pretty tree.
A: "Oh, what a pretty tree!"
B: "Then stay away from it!!!!"
A: "No, you're not gonna start again! This time it does not belong to the Sorceress!"
B: NO!!! Don't climb that tree, don't eat the fruits!!!
A: Who do you think you are? You're not our chief.
(he told them to leave it alone, but they didn't listen. They climbed up into its branches which then snapped shut, trapping them. The tree ran off through the forest).
I looked it up in the dictionary. In Russian the word "then" means "тогда", "затем", "потом" (= next, at that time, in that case). That's why I don't get its usage in the given context.