Parents must financially support their child until the child turns 21 years old or is emancipated. The Support Magistrate calculates how much support the non-custodial parent must pay to the parent with custody, and sets a schedule for regular payments.The Law Department assists local and out-of-state custodial parents in establishing an order of support from non-custodial parents. 1. Fill out a child support modification petition. 2. File the petition with the Family Court that most recently established your order. 3. Alimony and child support are very different. Learn what child support covers, how it is determined and the differences in tax implications. Alimony and child support are both based on income, but there are other factors. Click here to learn more. If a party has filed for a divorce or for legal separation, he or she can petition the court for temporary spousal support (alimony) and child support.