Need PC game suggestions similar to Zoo Tycoon
I have a couple of retired relatives with cognitive impairments who like PC games; however, the games cannot be too difficult. For example, Nancy Drew mysteries were a no-go. Zoo Tycoon was challenging at first, but with time became enjoyable. The computers are PCs with an XP operating system. I'm looking for older tried-and-true games that are less expensive, but will look at newer more expensive games too.
Any suggestions?