How to deal with a whiny kid?

I babysit a 6 and 4 year old, the 4 year old boy whines about everything to get his way and will even scream and get loud. Half the time I try to talk to him he gets louder. Sometimes I can distract him but other times he ends up getting his way. This morning he wanted soda and I said it's too early, he tried getting in the fridge and I kept saying no yet he got louder and louder, I tried ignoring him because that usually will work but it didn't. I told him if he has breakfast as well then he can have some. He took like 1 bite of his cereal and refused to eat more. Is there a better way to deal with this kid where he won't scream and whine?
How to deal with a whiny kid?
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