Parents are Rh +ve and child Rh -ve
Rhesus antigen (Rh-D) is inherited in an autosomal dominant pattern.  Therefore you are correct in your reasoning.  

Simple problems like this are often best worked out using Punnet Squares, shown below for the scenarios you have considered.



Because the inheritance pattern is dominant, if either parent was homozygous (DD) for Rh-D then 100% of their offspring will be Rh+ve.



In order to have a rhesus negative child, neither parent must be homozygous for the D allele.  You are correct that one possible scenario is a matching pair of heterozygotes:



In this situation 3/4 of the children are rhesus positive and 1/4 rhesus negative.  

There is an alternative where one parent is Rhesus negative and the other positive.  In this case there is one heterozygous parent and one homozygous negative parent:



In this scenario, half of the children are rhesus positive and half rhesus negative.