Baby can be said as 'akachan' in Japanese.
ひらがな と カタカナHiragana To (And) Katakana
As a person's name, ブリタニー (bu ri ta nii). As the name of French region ブルターニュ /bu ri taa nyu/ is used.
watashi no akachan for a baby koibito for girlfriend
otouto = younger brother otouto san WA _____ = my younger brother is _____ You call your little brother otouto. If it is a baby you can refer to it as akachan as well, but it seems a little distant.