Can two short parents have an average height child?

Possible. The expected height of kids would be average parental height + 2.5 inch for boys and -2.5in for girls. If either or both parents have genetic material on board from their families that should have made them taller, there is some chance that a taller child could be produced. Often the eventual stature of kids can be predicted in mid childhood using their bone maturity and pattern of growth.