With a science connection. OK, I admit not much of a science connection, but really, it's hard to find them.
For the adult, the obvious choice is this "Man in a Cage" costume, wherein a gorilla holds you in a cage. I'm not sure how much you have to pay the gorilla or if there are other options such as, maybe, an orang-utan. I'm sure this can easily be adapted to be a "Woman is a Cage" as you wish.
It is called the Man in a Gorilla Cage Costume and is available in fine costume stores on the east and west coast but probably not in the middle.
For the dog, the obvious choice is the Animal Planet Raptor Dog Costume. This will probably cause the other dogs to totally freak out. And cats. The cats will totally freak out. Or, even better, put this costume on your cat and see if the dog freaks out!
And for the little one, this frog costume should do the trick. It is called the Little Frog Infant Costume, but really, it should be called the Little Infant Frog costume because as far as I can tell it is a costume of a frog to be worn by the little infant. But perhaps I've got that wrong.
For intermediate age children, you don't need a costume. Do what I did when I was a kid, ever year and year after year: Get a cork and burn it. Let it cool down. Get your dad's oldest and most beat up jacket. Smear the black stuff all over your face to make you look like you have been out in the woods too long and haven't shaved, and wear the coat. If some wise-ass adult asks you what you're supposed to be, you say "Your worst nightmare. Just give me the damn candy!" and you'll be fine.
Many Halloween's ago I dressed as a flask of HeLa cells, wearing my "Henrietta Lacks Lives!" T-shirt underneath a dry-cleaning bag. But people kept asking me "Who is Henrietta, and why does she lack lives?"
I once had a cat that totally freaked out at a particular teddy bear. Not all teddy bears, just this one. Something about it convinced the cat that it was not only alive but also a deadly enemy.
And that's before I made the bear move.
Uh-oh, that apostrophe doesn't belong there...
Man in a Gorilla Cage Costume is amazing!