My kids that I claim and they are 18 & 20 years old and have part time jobs, they rather i not claim them so they get more of a refund back. Will that reduce my refund?

My children 18 senior in high school and 20 year old second year in college, both have part time jobs. I have always claimed them on my taxes, but they ask for me not too, so they would get a bigger return. How much will that affect my return??