Can the police enter your backyard without a warrant to look for a child in that area or the area around it?

A Salt Lake City police officer did that recently and there is some debate about whether it was proper. The police department is arguing that this was an example of "exigent circumstances" and they did what was necessary to recover the child. Others, such as myself, would argue that the police had no probable cause to believe the child was in that particular house or yard. Ultimately, this is an issue that courts will need to clarify.