Being an identical twin myself.. i have wondered about this alot. I found out that as myself and identical twin's DNA is an exact genetic match.. if we do have childern.. they will genetically test as half-sister's or brother. If however we were to have children with another set of exact identical twin males, our children may not look alike.. but would, in a DNA test, show up as full sister and brother and would probably look like siblings!! if my identical twin sister goes on to have children, they would, in a dna test, show up as my children aswell!!! strange eh!!