since they are getting mouthfulls of the stuff, i would suggest getting some leaf litter. you can buy it from many online vendors and/or some pet stores. you can also collect your own.

also you can bowl feed. it makes things MUCH easier. get a small glass bowl and put the crickets in there. for starters you can put some inside the bowl and outside until they get used to it. once they start eating out of the bowl, you can monitor how much they are eating per night, you wont have dead crickets laying all over the tank, you wont risk the frogs getting a mouthfull of substrate, and im sure there are many more plus sides that im forgetting right now lol.