ちゃん is the honorific you put on a child's name. So, who is this mysterious child you're calling red? When a baby is born, what color are they? You got it, they're all red. And, because you want to be nice and cute you add ちゃん to that. That's why あかちゃん is a baby.
If you know the reading of the kanji 赤 you should know the reading of this too.
A baby will be born in May.
This cute baby girl is Emma.
This is baby formula.