your call
depends on the dragon, can compact in the gut and cause blockages sometimes, especially if temperature is down a bit and gut has slowed down, they dont digest sand or bark and have to pass it through the system
smaller dragon, smaller gut. small particles have a greater effect than in an adult
in the wild they do eat the odd foreign matter, but in the wild mortality of juveniles is really high
lizards constantly test their environment by licking substrate rocks etc
sticky foods or a partially squashed insect can have large amounts of sand adhering to them
Once saw a large saltwater crocodile suffer badly then die, after autopsy discovered 15 kgs of stones and a handbag in its gut
as repto said at 5 hundy better to be safe than sorry, but that is your call