The child has a 50/50 chance of having red hair. They could also have brown, black or even blonde hair. Until the child is born, you don't know what the hair color will be. Even then it could change. They could have red hair, when they are born and later on it could change to brown.
Red hair is not a dominant gene, so the likelyhood is decreased by that factor. If the majority of the grandparents have red hair, chances increase. If grandparents are mostly blonde or brunette tho, the trait may skip a generation, depending on pedigree and inheritence patterns throughout family history. If grand parents r mostly red heads chances are about 70%.