My froglets miss a lot of flies too. It could also be short tongue syndrome. I think it was said to be related to lack of vitamin A. Just make sure you are supplementing their food and it will work itself out.
Do a search on short tongue syndrome for more info about that.
i noticed the frogs i raised from tadpoles were pretty bad hunters at first too. i would have to put the flies RIGHT in front of them and they would miss occasionally. they are a few months old now tho and doing just fine my guess is that they just need to learn how to hunt and it takes a bit for them to gain any skill! lol
I stuck a little flying gnat in with my frogs a couple days ago. At over a year old you'd think they'd be skilled hunters, but holy cow was it the most uncoordinated attempt at getting a fly ever. The fly flew off and the frog sat there scratching her head thinking, "What the heck? Did that thing just FLY?!?!" It tried a couple more times to get it before giving up...
When they're new to something sometimes they stink at it. When your frog hits the fly, does the fly stick?