I personally would prefer to see them eating whether it is live or f/t. At that young I think its more important to get some size on them before trying to switch them to f/t. I let my new girl get up to 400 grams on live and she switched without any problem to f/t just a couple of weeks ago. Just give them some time to grow a bit.
I would hate to see a hatchling get sickly from not eating. This is just how I do things.
Maybe someone with more expertise will chime in.