Do you have an estimation jar in your classroom? We have one that we use as part of our morning activities a few times a week. Ours has large buttons in it. I change the number of buttons it contains each time. The children get better at estimating how many are in the jar as the year progresses. I also change what items are in the jar periodically. The activity helps the children build number sense.
I created a poster and printables for the estimation jar activity.