Human babies in Japanese are generally referred to as 赤ちゃん　（あかちゃん） Baby animals get the 子- prefix to make them juveniles of the species. If you want to say that a human baby is like an angel, you might want to say 天使のような赤ちゃん I don't know if 子天使 is widely used, but I am sure it would be easily understood as referring to a baby angel. Alternatively you could say 天使の赤ちゃん too. Japanese people also use the English loanword エンジェル. You could probably say エンジェル・ベイビー We probably need to know about more about the context. Are you talking about a friend's cute baby, or are you writing a science fiction fairy tale?

For your information, you use the word 雛(ひな) when you refer to baby birds.