What's the best way to fatten up a leo? And are Phoenix worms any good?

[LizzyKoalaBear]

So both of my babies are about a year old and are still very small. The girl doesn't even move my scale and it's a small kitchen type scale. The other one barely moved it. The girl is pretty much missing all of her tail so that might be part of it and both of them are very active. So basically I want to know what are the best ways to fatten them up a bit and if the Phoenix worms are any good. Thanks in advanced for helping