Can parents who are b positive and ab positive have an a positive child?

Yes, parents who are B positive (genotype can be either BB or BO) and AB positive (genotype AB) can have a child with an A positive blood type. The possible combinations of alleles from these parents can include A (from the AB parent) and B (from the B parent), resulting in an AB child. However, if the B parent has the BO genotype, there's also a chance for an AO combination, leading to an A blood type in the child.