Obviously your parents are not experts otherwise you would not need to be here.
Your frog needs to see a Vet ASAP!!! This is not to be taken lightly. The infection your frog has could kill him if not treated. It will begin to spread and if not treated soon it could go beyond the ability for treatment to help him.
I'm sorry, but that is the truth. These animals are extremely sensitive and it is our respincibility to care for them once we bring them into our homes. They rely on our care to help them thrive. They are not disposable pets as was stated above.
They should be taken for medical care like any other pet whether it be dog or amphibian. Tell your parents he needs a Vet. There isnt much you can do on your own. He will need antibiotics and possibly force fed. A Vet can provide feeding syringes and a Critical Care formula to force feed the frog with to nurse him back to health.
Keep us posted.