Dependents earned income from part-time jobs in 2016.

For 2016, by daughter 23, and son 25, both worked part-time jobs. They each earned over $4,050 for tax year 2016. I believe this is the threshold amount Dependents can earn in 2016. I believe that because of the amounts they each earned, I can no longer list each of them as Dependents on my 2016 tax return. I believe they are now required to file their individual tax returns in order to get back what they paid in taxes, and because of the amounts they earned. Am I correct in this?