More commonly, "Ohhhhhhbabychild" (one word, despite red squiggly misspelling from various word editing programs such as Word
whom may never completely understand language enough to properly know that such words, amazing though they may be, are, in fact, words).
It can refer to either: (1) a term of endearment meant to sweep one off of one's feet, such as when love is in the air, and the one whom one loves makes them feel like (A) a child again or (B) so wildly awesome that the only adjective to describe anything in the near vicinity or circumstance is simply "every positive adjective!"
or (2) used (also generally as a term of endearment simultaneously) to sarcastically reference the oh-so-white undertones of the Black Keys
that try oh-so-hard to be black.
mmmmmbabychild i miss you so hard i could write a song about you, fly to mexico, form a mariachi band, and sing so loud that you'd come-a runnin all while shoutin 'I HEAR YE BABYCHILD! MAMA'S comin and she broughts you's a cassette mixtape of Babychild tunes for your ears and a bright red n gold fruit pizza to eat on my naked belly! babychild's comin!