They will not contact you about the application fee waiver, likely. You will file a FAFSA after the first of the year, which will show child support as funds received. You will probably be selected for Verification, which means you will have to supply all kinds of information on how you live. So start a folder where you collect photo copies of the child support checks and your mom’s bank statements. Are you on any kind of aid or free lunch? That will simplify the FAFSA reporting. However if you are verified they are going to ask for tax returns. You will indicate on FAFSA that you mom is not required to file taxes, I believe. You may have to submit some kind of Non Filers Statement. See for example this page for UC Davis on forms you may be asked to submit. You want to be prepared so that your aid is not delayed.
http://financialaid.ucdavis.edu/undergraduate/forms/verification.html