When Casey's hair starts to get longer, Raph will use his bandana as a hairtie
Kids also have a tendency to pick up positive behaviour if it rewards them with positive attention, so I like to think Casey started replicating chirping before he started saying things like "I'm happy" or "I love you".
Also, Raph doesn't stop wearing Casey Junior's baby slink until Casey is about 6, and can no longer fit in it. Donnie commented once on this ordeal, and Raph only demonstrated a 4 year old Casey Junior huddled up comfortably against his big papa.













