Nope.
Prawn is a very inapropriate food source, more so if it´s the only one they get. I wouldn´t even offer it sporadically..it´s just not adequate for a fresh-water amphibian. You really need to get them something else, right away. Earthworms are the best food you´ll find, and they can and should be the staple of their diet. You can also find other suitable foods, to offer variety, in pet-shops or buying them online (like frozen bloodworms, crickets, waxworms, Daphnia...). You can also try bait shops, or even dig some worms yourself if you have access to a chemical free area.
I don´t mean to be rude, and i realize you are trying, but if you can´t provide them with what they need, you shouldn´t have bought them. Those animals have been torn from their habitats, transported in terrible conditions where many have died and many more fallen ill, and sold for a ridiculous price....the very least they deserve is a decent captive home. I´m sorry if it comes across as agressive, i realize it´s a mistake most of us have made, but i´m trying to wake you up a bit and make you see that now that those animals are your responsability, you need to improve their care.
You can try to send me the pictures and i´ll upload them for you. I´ll send you my e-mail in a PM.