A lot of different kinds of animals lived in ancient Egypt. Wild animals included crocodiles, who lived in the Nile River water (and there are still lots of crocodiles in the Nile today, too!), and lots of water birds like herons and cranes and ibises who lived along the banks of the Nile (and still do today).
People were most afraid of the hippopotamus, which was a fierce animal that lived in the river. Hippos look cute when you see them at the zoo, but they kill many people every year even today.
On the land, there were wild gazelles.
The people who lived in ancient Egypt had tame (domesticated) animals as well. Some of these animals were useful for farming or transporting things, like donkeys, camels, dogs, pigs, cattle, and sheep and goats. Most of these domesticated animals came to Egypt from other places: donkeys and sheep probably from West Asia, cattle and pigs and horses probably from Central Asia.
Other animals, like cats, were kept mainly as pets. The Egyptians may have been the first people to keep pet cats, perhaps starting around 7500 BC, but it's also possible that cats were first kept as pets in West Asia.
Learn by doing: go to the zoo and check out hippos and gazelles and crocodiles
More about the environment of ancient Egypt
Farming & Food (The Ancient Egyptians), by Jane Shuter (1998). For kids.
Everyday Life in Ancient Egypt, by Lionel Casson (revised edition 2001). Not especially for kids, but pretty entertaining reading, and Casson knows what he's talking about.
The Cat in Ancient Egypt, by Jaromir Malek (1997).