Help w/ Biology HW- How can you tell genotype from a pedigree?

Well clearly the disorder is recessive, as it shows up in one of the children without being expressed in either parent: let's say "A" is the dominant, normal gene and "a" is the recessive, disordered gene. In order to have produced a child with the recessive gene, both parents must carry it: their genotypes are Aa. The third child, of course, has aa, the only genotype which expresses the disorder. The other children might have either AA or Aa-- we don't know because their parents had the ability to produce both and we only know their phenotypes.