While planning the lesson plan for third grade, it is very important for a teacher to have an idea what the students already know before introducing any topic. Before introducing the Topic "What are germs?", the teacher she should be ready with a list of questions beforehand and mention them in her lesson plan. Assessing the previous knowledge of the students gives a strong base for an effective teaching.
Questions like, 'What are insects?', 'Have you heard the word germs?', 'Have you seen insects/germs?', help in approaching the topic that you have to introduce in the class.
The teacher should skillfully introduce the topic in the class after having an idea about the knowledge of the students and try to link the answers given by the students to the present topic.
For example, when you ask, "Have you seen an insect?", students will come up with many answers. At the same time when you ask if they have seen germs, they may not be able to say "yes"!. So you can reinforce the fact that the germs are so small that we cannot see them.