Your child is now starting to develop the understanding of science and has began to learn scientific concepts that he can see around him. You child must have learnt these skills during playing, while at home and also during school through the lessons. Your child is now able to differentiate between living and non-living things and how the natures conditions like rains, thunder, cold, summer, would impact their lives. So, keep up his interest in the simplest of way possible.
What you need to know
Your child is now aware of the nature around them and ask questions about the insects, birds, plants etc. they see and observe. If you ask them to write they can draw straight figures of the plants, lake/water bodies, mountains as they imagine and learn along. Your child at an age where he must be introduced to germination and they will show interest in the seeds growing into saplings and then plants. You can sow seeds that grow fast in your home pots and make them water it and nurture their curiosity on how the seeds grows into plants and what are the different benefits from different plants & trees.
At this age your toddler is a keen observers and record everything in mind. As a parent, encourage his/her questions. If the your child is not asking, encourage him to ask and when they do so, answer them correctly and as is in a way they can understand. Do not give false information thinking they would not understand or get the concept.