Carolyn, there may indeed be tons of earthworms out there but they are never fed to nestlings except in very dire circumstances. Earthworms make nestlings very sick and can kill them.
Go ahead and stick with dried mealworms. If yours love them there is no reason to switch. Just remember not to give them out with a heavy hand. Too many are calcium depleting and they do need a healthy dose of natural food everyday.
Gin
Atlanta, GA