bubby · noun1
Likely a babble word; compare dialectal German Bübbi (“teat”). Some older references connected the word to French poupe, but this is considered "very doubtful" by the OED. Compare Latin pūpa (“little girl”).
bubby · noun2
Perhaps from brother, as pronounced by young children who are not yet able to properly pronounce its complex consonants, but alternatively perhaps from Pennsylvania German; see bub. Compare sissy.
bubby · noun3
Variant spelling. (From Yiddish.)
Etymology from Wiktionary, CC BY-SA 4.0.