Ryan Veeder’s Captain Verdeterre’s Treasure would be a good game for kids. There’s not much objectionable material (unless you think pirates are a no-no), and the resource management puzzle at the heart of the game could be considered educational. Also worth a look is So You’ve Never Played a Text Adventure Before, Huh, by the same author. It’s an IF tutorial, like the title suggests, and kids might find it a fun way to learn how to play parser-based IF, or text adventures.
Other than that, there’s always perennial favorite Lost Pig, as well as older games for children, like A Bear’s Night Out, or Mother Loose. If you’re teaching in a religious context, Cana According to Micah, a goofy retelling of the water into wine miracle, may be helpful as, say, an introduction to the Gospels. If you aren’t, then Sunday Afternoon, by the same author (his real name is Christopher Huang) would be a great look at late Victorian society from a child’s perspective, as well as World War 1.
Finally, there are a couple IF that center around wordplay; these may be too difficult or inappropriate for the age group you’re looking at, but I’ll list them off in case it helps:
Ad Verbum by Nick Montfort (mostly unrelated wordplay gags)
Shuffling Around by Andrew Schultz (anagrams)
A Roiling Original by Andrew Schultz (anagrams, sequel to the above)
Patanoir by Simon Christiansen (metaphors)
Goose, Egg, Badger by Brian Rapp (verbs that are also nouns, and vice versa)
The Gostak by Carl Muckenhoupt (game is in English but uses an entirely different vocabulary, hard to explain in such short space)
That’s far from an exhaustive list, but it should be a good start. I might come back later and recommend some choice-based/Twine IF as well.