It didn't stand out to me, only because whether the older kids were home or not, Orrin and Orson are still the "youngest two". Also because I have 8 kids and we always refer to them by birth order instead of names, if any of us are talking to someone that doesn't know all the kids, their names or ages. Example: if talking to a family member "Name, name and name all went to the park today". If talking to someone that doesn't know their names/ages: "The youngest three went to the park today". I think it might be one of those weird "this is common in large families" kind of things.
jmo