Keep It Hands-On
Science experiments for young children should be hands-on activities. Start with a big book to explain a concept, but then make sure the activity or experiment is safe, concrete, and hands on. Kinesthetic exploration is the key to a greater understanding of early science concepts. As a rule, the activity should be able to show "same day results". Growing plants, measuring rainfall, or growing a crystal takes such a long time, the children might lose interest. If you decide to do these kinds of activities, make sure the developing activity is visible in the classroom and that you talk about it each day. Choose fast growing plants, like grass. A picture graph or other visual should accompany the activity to provide a visible show of progression.
Explore the wind with bubbles and child-made windsocks.
Use magnifying glasses to take a closer look at bugs on the playground.
A field trip to the zoo or local farm is an awesome study of early zoology. Many zoos and farms offer petting opportunities for actual interactions with animals.
Winter science fun might include bringing a bowl-full of snow inside and melting it to discover the composition of snow.
Regardless of what activities you choose, making them fun, concrete, and relevant to their world will reinforce the concepts you are teaching in the early learning environment.