Bracken ferns are the only fern i know that has a health warning against pet animals. Most ferns have toxic fiddlehead fronds though (unopened new leaf) but only if chewed and ingested. Plain and direct ingestion doesn't seem to affect animals that don't chew food (like turtles and fish. Yes, i personally tried feeding it lol). Great majority of ferns have tough root systems as well (wooden roots, even) so worrying about your frog destroying the roots should not be a concern.

And oh and about wandering jews, they're safe but they have brittle stems so place them where your frog won't encounter it directly or else you'll get chopped plants lol