Can White's Tree Frog's eat each other?

I have a 40 gallon tropical vivarium with 4 whites tree frogs, I bought 4 of them together at petco. They gave me 2 fully grown ones, they are big. then one medium sized one, and one that still was pretty small. They all like to hurdle together in the corner of the tank towards the top. Well for about 3 days now I can not find the little guy anywhere. I was researching and read that you should have similar sized ones together which I did not know. Is there anyway the fully grown big guys could of eaten the little baby? I've had small goldfish go missing from the water in the tank and i'm sure its them eating the fish too. I feed them 30 large crickets every 3-5 days with vitamins. So its not like there being underfed. If anybody knows if they will eat each other then please let me know! The baby was about the length of my pinky finger, maybe a little smaller. So hes pretty small and the fully grown guys are huggge.