Mary: It's a secret garden.
Dickon: Secrets are safe with me.
Colin: What do you say in India when you want people to go?
Mary: You say, I have spoken, all depart.
Mary: Please don't send me away, I won't do any harm.
Lord Craven: Harm? What harm can a child do?
Colin: I'm not sour.
Mary: You are strange.
Martha: Hey, I know that.
Ben Weatherstaff: But aren't your legs all crooked?
Colin: Who says my legs are crooked?
Mary: Nobody says that.
Mrs. Medlock: God! Look at your legs, they are swollen and red.
Martha: I don't know when exactly your uncle will call for you.
Mary: My uncle? Mrs. Medlock said he wouldn't want to see me.
Martha: Ah but he does.
Colin: Hair is dead.
Mary: If hair is dead, why does it keep growing all the time, even after you're dead? Well, maybe not your hair. You'll probably be bald.
Colin: Don't be daft. I'll die before I'm ever old enough to go bald.
Mary: I hate the way you talk about dying.
Colin: Everyone thinks I'll die.
Mary: If everyone thought that about me, I wouldn't do it.
Mary: Can I have a bit of earth?
Lord Craven: A bit of earth?
Mary: To plant seeds in. To make things grow.
Answer: Mary is told by Dickon that Colin was born early, and Martha even says that he was born very small and weak and no-one thought that he would survive. I think his premature birth made them believe that he was going to be a sickly child.