The challenge and campaign modes are similar though have different style of goals.
All of the modes of play can be experience cooperatively. If you're looking for a greater challenge Zoo Tycoon extends into a Campaign mode and a challenge mode. In terms of playing with younger kids, Zoo Tycoon offers a 'free' mode where you are given unlimited funds and can quickly level up your zoo keeper and see all the animals at your disposal. Up to four people can contribute to a zoo both in realtime and asynchronously. All that said Zoo Tycoon is a great co-op game, whether you're just playing pass the controller co-op on the couch (like I played with my kid), or you are taking advantage of the game's unique online co-op modes.
