I realize you are probably looking for a more expert opinion than mine, but from what I have read and seen, if it's smaller than they are and it wiggles, they will try to eat it. I get the feeling the smaller toadlets would try to eat the crickets. It's just instinct at work. If they were mine, I would probably keep them all on fruit flies a bit longer, for two reasons:

-It's more convenient for you only having to worry about 1 type of food and 1 feeding area/time
-It does them no harm to feed them more of a smaller food item, but giving them something that some of them might not be able to swallow could be problematic.

I know the fruit flies are expensive and a pain compared to crickets. Hopefully the size disparity won't get to the point where they start looking at each other as food. That's the larger concern in my book.

One fellow's opinion...