I'm looking for a book that was read to me by a fourth grade teacher in the U.S, year 1999 or 2000. The paperback (could have been Scholastic, not sure) was battered, so it wasn't a new book at the time. The teacher also read Roald Dahl's The BFG (1982), so I wouldn't be surprised if this book was from the same era. Characters: There were two children, a boy and a girl (maybe siblings, maybe not (I think not, can't be sure)), and an adult male. The adult functioned as a caretaker in the novel, but I can't remember his relationship to the children, though he may have been their teacher. Plot: Begins as realistic fiction, but then there is a device (I believe it is a device, rather than magic) that transports these human characters to another place OR time. I can't remember if they go back in time or to another planet (or both!) They find themselves in a primitive forest/rainforest/jungle with huge trees and dangerous flora and fauna. Here they meet a non-human character, a creature, who I believe was pink in hue and had a trunk like an elephant, a trunk that I remember quite specifically being described as "translucent" (it's how I learned that word). I think this creature (who I believe was male) was more the size of a dog or pony than an elephant, though. This creature becomes their friend, and assists them in finding their way back to their proper time/world.
That's all I remember. Any help in finding this title would be very appreciated!