Does the clay change color (get lighter, darker, etc.) if it is baked
properly? Will sunlight fade clay or make it brittle/dry it out?

Clay colors with a translucent base darken during baking. Avoid this by adding
white to opaque the color a bit--it only takes a little chunk. Some baked
colors ARE fugitive in sunlight, such as purples and reds. This pertains to
permanent outdoor pieces, NOT to jewelry worn during daylight hours!!

Is there anything about working with clay that can be harmful to pets?

Clay that is eaten is not TOXIC, but can form intestinal blockages, as do
rubber bands, etc...so try to keep from serving them up to your pets. Or to
your friends!
Sarajane

Sarajane's Polymer Clay Gallery
http://www.polyclay.com