General rules, use them as you like:
Cobble as a drainage layer.
Moisture retaining bedding at a depth that the frog can bury itself.
A water bowl, sunken all the way into the bedding so they can't burrow under it.
Maybe a hide.

That size tank is good size for an adult. Just make sure that the juvenile eats when he is in that tank. (Hand feeding, feeding in a separate container, etc.)

Best,
Alex