The new magazine Wondertime (a Family Fun publication for parents of toddlers and preschoolers) has named the book Actual Size by Steven Jenkins as "must have" on their recommended toy and book list. You can check this great book out from the library...it is a great way for kids (and adults!) to visualize the "actual size" and weights of a variety of animals as the unique collage-style artwork shows the animals (or just parts of them) at their real sizes. For example, giant squids can be up to 59 feet long (counting their tentacles) and the book shows just one giant eye (up to 12 inches across!) on the page.
If you like this title, you might also enjoy Prehistoric Actual Size (also by Jenkins) and the books in the Life-Size series by Daniel Gilpin including Life-size sharks and other underwater creatures and Life-size killer creatures.
Gigantic!: How Big Were the Dinosaurs? by Patrick O'Brien is another favorite title that helps people (especially spatially challenged people like me!) understand the enormity of dinosaurs by comparing them to familiar objects, structures, or machines.