Where does lady Macbeth call her husband a child and why?

This is probably when L. Macbeth calls her husband a child because he refuses to fetch the bloody daggers from Duncan's room. Macbeth is all scared to look at the body again because what he has done. L.Macbeth says the dead like a painting, can't hurt him; only children are afraid of scary paintings. Check the quote out,

Infirm of purpose!

Give me the daggers: the sleeping and the dead

Are but as pictures: 'tis the eye of childhood

That fears a painted devil. If he do bleed,

I'll gild the faces of the grooms withal;

For it must seem their guilt.