Noun
あかちゃん
ぶじに、女の赤ちゃんがうまれました。
The baby girl was born without complications.
このかわいい女の子の赤ちゃんの名まえはエマちゃんです。
This cute baby girl's name is Emma.
あなたの赤ちゃんの頃の写真が見てみたいわ。
I want to see a picture of you from when you were a baby.
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.