Before formal subtraction, children explore separating or taking away from a group. "I have 5 blocks and take away 2. How many are left?" This concrete experience builds understanding of subtraction.
Use objects that can be hidden or moved. Start with small totals (5 or fewer). Hide some objects and ask how many are left. Use language like "take away" and "left."
Children may not remember how many they started with. They may recount everything. They may not understand the relationship between the original group and the separated groups.
You've learned that every group of objects has a cardinality — a count that tells you how many are in the group. Separating sets builds on that idea: what happens to a group's count when you take some objects away from it?
Start with something concrete. Imagine 5 strawberries on a plate. You eat 2 of them. Now count what's left: 3. The key idea is that the group you started with (5) is still connected to the parts. The 2 strawberries you ate and the 3 remaining strawberries together make the original 5. This is called the part-whole relationship: a whole group can be split into two parts, and the parts always add back up to the whole.
"Taking away" or "separating" is the action that turns a whole into a part and a leftover. To figure out how many are left, you need to remember two things: how many you started with (the whole) and how many were taken away (one part). The number remaining is the other part. With small numbers, you can find this by counting the objects that are left. You don't need to count everything again from the beginning — just count what remains after the separation.
As you practice this with blocks, fingers, or counters, notice the pattern: the group you start with always gets smaller when you take things away, never bigger. And the part you take away plus the part that's left always equal the whole you started with. This is the big idea behind subtraction, which you'll learn to write with numbers and symbols next. For now, the goal is to feel this relationship with real objects — to know in your hands and eyes that "take away" changes the count in a predictable way.