I am a natural resources interpreter and have done an inordinate number of public and school programs so maybe I can give you a couple of pointers. Of course, these are pointers, so take them or leave them as you will.
1. Introduce yourself and your background in your subject. This gives you credibility, especially important to older kids.
2. Bring a helper to hang on to or calm your creatures. Even the tamest critters in a room full of excited kids can be a handful.
3. Choose a theme to talk about. "Owning animals is a great rewarding experience but comes with responsibility" or some such. A theme makes a program more memorable. If it were me, I'd do something like this: State your thematic intent, and then talk about the feed and care requirements, technical stuff, etc. Finish with how rewarding raising healthy happy animals really is, so you end on a positive note that drives home your theme.
4. Draw out a couple of main points to talk about. Depending on how you are every day, you could easily under or over shoot your time goal.
5. Older kids often get this "too cool for whatever you're talking about" thing going on. Trust me, they will soak up your info even if they seem like their heads are turned off. Don't let that phase you.
6. Never say no when someone answers a question incorrectly. "That's a good guess" or "In this case, we..." or something like that really helps keep people engaged. Saying "no" when someone answers your question can turn an audience off.
7. Contrarily, if someone says something like "I've heard goats eat tin cans," go ahead and say "No," but follow up with something they do eat and a positive somethingorother.
Anyway, hopefully this helps. Like I said, take it or leave it, but these are things I use all the time in the field. Good luck and have fun!