So Kyle was dropped into the breast itself by the growing hole? (As we know, the breasts hold milk, so they would most likely be hollow somewhere) Is that what's implied?

If this is true, then I like the idea. But also, if the hole resealed, how could she reach in and grab him out?

If you want to make it open, good idea, although I think you need to keep writing. Perhaps make the chapters longer. You need to expand on the body adventure. Perhaps a more "inner" body adventure is in order (but don't try it if you don't want to. Some people have tried and it wasn't very good (to me))

Also, avoid Toilet at all costs.