My oldest two are completely opposite. There both Girls and are 21 months apart in age. My oldest is Tall and skinny, My middle daughter is short and a little chunky . My oldest looks like shes nine when shes only 4 and mu middle daughter looks like she 1 and shell be 3 in the next few months. Personality wise there pretty far apart too. My oldest is more of the go with the flow , gets along with everyone and pretty easy to please type of child. My middle daughter is very high maintenance , she doesn't like people and is pretty shy. She is a drama queen. Another difference is my oldest is a very picky eater where as my middle child love all types of foods and will try just about anything and my oldest loves car rides and my middle daughter hates them and barely makes it to the store 5 minutes away before she freaks out. Also my oldest has a speech delay so my middle daughter sometimes speaks better then her sister even though shes almost two years younger then her. So far my son whose 27 months younger then my middle daughter is in between them both .