but I don't know if it's enough to make a single animal rabid.
That's why you include a female animal. It will breed in the cage, and the offspring will be rabid. I'm starting to believe that a 2x2 or 3x3 would be much preferred. The issue, still, is insanity. Keeping the child from going mad during the whole process will be quite difficult. Investing in masterwork platinum chairs may be in order. Or perhaps restructure the entire thing to allow for statues. I prefer the hanging cage just because of the terror it invokes, but a raised platform with statue walls would be very easy to admire, and if it had a table and chair, then the child could enjoy a royal dining hall. A bed and they enjoy a royal bedroom. A 3x3 would allow for a bed, chair, table, quantum food pile, central waterfall grate, and a few tiles left over. I'm debating the use of a 2x2 room with a downstairs 1x2, that's room for an upstairs chair, table, food, and stairs, and a downstairs bed and stairs.
Also, I have no idea how to handle the moods, except to remain hopeful or allow a temporary escape. But who wants to let the buggers out?