For sizes I use the story The Three Bears. After reading the story to the class, I give them a 12×18 sheet of construction paper and sets of three things: The three bears (papa: big; mama: medium; baby: small); three beds, three chairs, etc. The children then glue Papa Bear, Mama Bear and Baby Bear onto each section of the construction paper. They then add the other pieces according to their sizes. They can then use this paper to retell the story.
This idea can be used for little/big and in/out lessons. I cut out a big and little bear for each child out of construction paper. The big bear had a pocket on his tummy for the little bear to fit into. Each child colored their own bears.
Use a long piece of elastic sewn into a circle (big enough for the whole group to put 2 hands on it) to talk about big, bigger, biggest-have the kids hold the elastic and walk backwards as they stretch the band-you can also use this to talk about circles or just for a fun movement activity. it is fun to stretch the band as tight as possible and have all let go on the count of 3. This is also a great lesson in cooperation.
I use this as a math project with my class when talking about size. Use the teddy bear counters that come in different sizes and colors. Have the children separate them in to groups of each size. than you can also have them make patterns of big and small mixed together.