Ive been using locusts as my beardies staple diet since I got them at 4 weeks old. Make sure you get small locusts for 3 week old dragons though. I made the mistake feeding mine meduim to pretty damn large at the beginging for 2 weeks. There perfectly fine though but you run the risk of them not being able to digest it but there little troopers and in the wild im pretty sure they'd go for even bigger ones if they were around.