What to do?

This is how I keep finding my oldest and youngest in the mornings. Not good. I have explained to Olivia in a zillion ways why it's not good for her to put him in bed with her, but she just can't resist him when he's crying her name and sad. He is very irresistible when he's sad. Every night I say, "Ian, you need to sleep in your own bed." He smiles and says, "No! Ya ya" (which translates to Olivia). What should I do??? I don't even hear him cry, she takes care of things that quickly. It's nice of her, really, but such a bad habit. Oh dear...