It's the perfect answer to National Siblings Day. Only children, this day is yours! #NationalOnlyChildDay #OnlyChildDay #NationalSiblingsDay #birthorder #brothers #sisters #holidays #parenting #children #kids #boys #girls #Elvis #Adele #FrankSinatra #tv #movies #music #politics #celebrities #AliciaKeys #sports #TigerWoods #RobinWilliams #NataliePortman #CharlizeTheron #FDR #Roosevelt #DaVinci #JohnLennon #AlPacino #CarolBurnett #GeraldFord #MatthewPerry #BarackObama #Obama #RobertDiNero #science #study #studies