Don't worry about them, they'll be fine.
This year? Prune them in the fall after they go dormant. After the 1st frost is a good time.
These babies flower on new growth, so we don't want to remove new growth, right?

Now, they'll just put out more growth. Buds haven't formed, so you'll be fine. What kind did you buy? These have leafed out extremely early.
C.

I have read in a couple of different places that if you have any concerns about your crepe myrtle being hardy, it is safest to prune in early spring. I did that last year and still had lovely blooms.

You'd probably have lovely blooms anyway, because it's hard to kill them.
I know that since I began my obsessive collecting, I've read and tried different advice. To be fair, it might differ a bit per zone, but I don't know.

Mine have absolutely been prolific since I followed the advice to prune when dormant. They also put out fewer suckers trying to make up for the missing piece, so there is less "spidering" of the limbed area.

What type did you buy, which has nothing to do with the pruning? It's just that they've leafed out so early, it's very interesting. None of my 32 varieties have begun to do so and some I don't expect to start until the end of May!
C.