I'm the Biggest Thing in the Ocean by Kevin Sherry is a fun read, and it supports discussion of size comparisons. I also like to read any book about apples and then do an apple tasting activity using green, yellow, and red apples. As we taste each color, I ask how many in my group liked that color apple, and I color in a square on a column for that color apple. Then we taste the next apple. The end result is a bar graph and I show the children how to read it to see which color apple was most liked by our group. Another book I like to use is Measuring Penny by Loreen Leedy. It's a little advanced for this age group but you can work with it, and talk about ways to measure things, using unit blocks, tape measure, yardstick, and ruler.
ECE teacher, mother of 3, grandmother of a whole bunch