These special objects need not be expensive or elaborate. The important part is sharing information and experiences. Never underestimate the importance of good conversation and information to the development of vocabulary. Label, label, label. Give your children as much vocabulary as you can.
Most preschoolers know all the names of dinosaurs that most adults can barely pronounce.
Their minds are like sponges. Take each new experience you have as an opportunity to learn new words. When you visit the auto shop to get a new muffler, talk about mufflers, tail pipes, exhaust systems, and welding. When you visit the greenhouse to choose new plants for the garden, talk about marigolds, impatiens, zinnias, and geraniums. When you make a new recipe, talk about woks, peanut oil, soy sauce, bean sprouts, water chestnuts, and pea pods.