J.,
Coming from a teacher... it's never too early to expose them to MEASUREMENT... The tub's a GREAT place to start. Get them a set (or several! in different shapes and colors!) of measuring cups and spoons. They can have fun in the tub counting the teaspoons in a tablespoon, Cups in a pint. Look at how many 1/4ths is in a 1cup...and etc... They might be too young to understand everything, but it's certainly a great place to start exposing them... and measurement is always a challenge in our math curriculum.
Side note: Drop a $0.99 retractable sewing tape in their stocking, and on Christmas Morning you can keep your school-agers busy measuring everything from the christmas tree's height to the hamster's tail...PLEASE, get one with Metric as well as customary measurments; and keep it going all year.
Measure the dog's toenail before you trim, your child's earlobe, dad's nosehair(ewww, but the kids LOVE that sort of thing...LOL), the valve stem on the car, wiper blades, tire tread/width. Circumference of the tree in the yard, height of the fence, or the length of the grass... The diameter of the dryer opening. Area of the french toast for breakfast, length of green beans. Measure EVERYTHING...
You child's teacher will probably nominate you for the golden parent award!! Keep a measurement scavenger hunt handy for rainy days. Make a list of things to measure and send your school age kids on the hunt. It'll keep them busy AND learning at home. You can move from straight measurements to figuring the area of the bed, for a new quilt, and the volume of the bathtub or aquarium. These are HARD concepts for us to get across, but so much fun to play with at home.
:-)
T.