L and E are 30 months old.
Yesterday we tried an activity called "Blocks in Socks". It was loosely inspired by an idea in this book, with a lot of my own variations:
First I put one, two, or three 1-cm unit blocks in a (clean) sock, and invited the girls to reach in the tell me how many blocks were in the sock. They had fun guessing and subsequently pulling the blocks out to count them, but didn't get this one right. I love that this was challenging for them and we can redo this activity later.
Then I filled four socks with different amount of blocks (I wanted there to be big differences so it was something like 5, 10, 20, and 30 blocks). Then I asked the girls if they could feel the outside of the sock to determine which one had the most blocks and which had the least. Then we lifted them out to see which was heaviest and which was lightest. They really understood this concept well.
To check our answers, we emptied the contents of the socks into oversized test tubes, and discussed the differences between the amounts and how we can use visual discrimination to compare amounts instead of counting.
There were a lot of skills involved in this process including screwing the test tube lids on and off (L has been doing this for a while, but E is finally figuring it out), and figuring out how to transfer blocks from the socks into the test tubes without spilling them on the floor. We also shook the test tubes and listened to the sound they made. I got out the scale and we weighed the groups of blocks. They understood the concept that the heavier side will be lower. Then I let them play with the scale all on their own, and they had fun putting various objects in each side. E really enjoyed putting objects in the little drawer too.
I'll definitely revisit this activity a couple more times as they get older, but overall it provided over an hour's worth of fun exploration, making it a success.
UPDATE: I was so inspired by how much my kids enjoyed early learning games that I created the La La Logic Critical Thinking Curriculum for 3-6 year olds, which includes online brain challenge games, printable worksheets, enrichment activities and more!