I'm guessing you are talking about the type of child seat that is anchored by a seat belt?
Few child seats are designed to be effective unless they are either forward-facing or rear-facing, so that eliminates any seat belt positions that are on the sides of the RV, e.g. the typical RV sofa. Some RVs have dinette seats that have seat belts, though that is less common because of the proxiity of the dinette table. The table should probably be removed (many are designed for eack take-down) if you want to use the dinette seat.
You may want to consider adding a seat belt, perhaps in the floor of the center aisle, specifically to anchor a child seat. A bolt through the floor with a large (3 inch?) washer or backing plate on the underside will hold it nicely. It usually isn't too hard to add such a belt, as long as you are somewhat flexible about the exact location.