The children are said to have been struggling with the loss, but their coach says playing baseball together has helped them honor Castillo's memory.
The nearly weeklong search has also been frustrating for divers who want to help Castillo's family.
"Really want to find him," said Officer Jack Hayes of the Marine Unit. "I want to provide the father, the entire family with some closure. I can't even imagine what it would be like. So, I and all the Marine Unit officers want to find the victim."
The water is extremely murky, and divers have only about two inches of visibility.
The boy's father, Willy, donned scuba gear and dove into Chicago River Saturday morning to search himself before police arrived.