It's really not clear what you want to do. You may be better off speaking to your own professional.
If only your child lives there, you don't have to charge rent. It's just family helping family. And trying to declare it as a rental could cause tax issues unless you rent at fair market value (what you would charge a stranger.)
If you want to allow a roommate and you plan to charge rent, then you need to talk to an attorney about the condo association rules, rental contracts, and so on. You can rent 1/2 the home to a stranger at market value and let your child live in the other half for free, or you can rent to both at fair market value. If you charge less than fair market rent, your ability to take certain rental deductions is limited. On the other hand, doing a formal lease with your own child at full market rent may not be something you really want to do.
You have to start by asking yourself what is really going on? You bought a second home, and your child lives there temporarily? You bought a home for your child? Did you plan on a roommate situation?
