Two objects that are similar are not necessarily the same. For example, there are many kinds of beans, all going by different names and having different physical properties. Purchase several types of dried legumes, such as peas, lentils, peanuts or garbanzo beans, and mix them up. Give a small pile to the children and have them separate the elements and then explain why each is different or similar to the others.
For this activity, choose a single species of animal, and ask the children to compare it to a different species of the same family. For example, penguins are birds, but not all birds are penguins. Read the children a book about penguins, or watch a movie about them, then ask the children to think about the types of birds they've seen while playing outside. If you wish, you can make a Venn diagram by drawing two large overlapping circles, one for penguins and the other for another type of bird like a pigeon. Write the differences in the large circles and the similarities in the overlapping area. Organize the information using pictures or stickers to illustrate actions such as swimming and flying.
Show the children two pictures of different people. Each person will have characteristics that make her the same or different. Ask the children questions that help them pick out the details you want. For example, ask these questions: "Is one a man, or are the pictures of two women?" "What color hair does each person have?" "Is one tall and the other short?"
Show two or more pictures of people dressed for different professions. Firefighters, police officers, construction workers and postal workers are good examples of professions with easily recognizable uniforms. Ask the children to tell you specifics about each job, such as what each person does during a day on the job. Once the differences are identified, task the child with finding similarities between the jobs. For instance, a firefighter and a construction worker are both likely to use a ladder. Police officers and postal workers are both people whom the children are likely to see in their neighborhoods.