Sharing the swings
At recess, one line for the swings has 5 kids and the other has 3. You glance and know the first line has more, so you join the shorter one. Comparing 'more' and 'fewer' is something you already do without counting every head.
Bigger, smaller, or the same
To compare two groups, we can match them one to one or count each. The group with the larger count has more; the other has fewer. If the counts are the same, the groups are equal.
Further right is more
On the number line, the number further to the right is always the larger one. 8 is right of 5, so 8 is more than 5.
Simulation · Number-line explorer
3 + (-5) = -2
Place two numbers and see which sits further right — that one is greater.