ZackSull'IsolaAfter crashing into the ocean, Mr. Eko carries him to shore, when he calls out for his sister and points to his sister still floating in the water. Mr. Eko pulls her to safety. Ana-Lucia sees her and performs CPR, saving her life. ("The Other 48 Days")
After saving his sister from drowning, Ana-Lucia takes it upon herself to become a maternal figure to both Zack and Emma. On the first day after the crash, Mr. Eko asks Cindy if she can look after Zack and Emma while he takes the dead bodies out. Emma had a teddy bear with her on the plane, that Zack held onto while Emma was hurt.
They were seen at Donald's funeral, both hugging Ana-Lucia and looking sad. They were both, however, taken on Day 12 by The Others. ("The Other 48 Days")
Over a month later, after they were kidnapped by the others, Zack was seen by Jack along with his sister and Cindy, holding the teddy bear. As they leave Zack looks at Jack angrily. ("Stranger in a Strange Land")
When Kate finds Jack at The Barracks, she asks "And the people they took...the kids?" Jack confirms that they are safe. ("The Man from Tallahassee")
He is briefly glimpsed along with Cindy and his sister Emma after Ben shames Locke due to his failure to kill his father. ("The Brig")
Fonte Lostpedia