Can an O positive blood type father and an A positive blood type mother parent an O positive blood type child?

Yes, this is very possible, assuming that the mother's genotype is AO (she has genes for both A blood and O blood). Type O blood is recessive. If a person inherits the genes for both O type blood and A or B type blood, they will exhibit type A or type B blood, respectively. However, even two parents, both with a dominant type of blood, have a 25% chance of producing a child with type O blood (if both of them had the recessive gene for type O blood).