How do I implement a complex table constraint?

I have a table similar to the following:-

CREATE TABLE [dbo].[child_table](
	child_id [int] IDENTITY(1,1) NOT NULL,
	child_status [varchar](25) NULL,
	parent_id [int] NOT NULL,
	CONSTRAINT [PK__child_table] PRIMARY KEY CLUSTERED 
	(
		child_id ASC
	)
)

Each parent_id may have one or more child_id's. But only one child (of each parent) may have a "child_status" of "Active". Is there a way to enforce this in TSQL (e.g. with a CHECK CONSTRAINT or RULE), I can't find a way to do this.

Thanks